| Schedule of Available-for-sale Securities [Line Items] |
Available-for-sale Securities, Amortized Cost | Available-for-sale Securities, Gross Unrealized Gains | Available-for-sale Securities, Gross Unrealized Losses | Available-for-sale Securities, Debt Securities |
2007 | | Debt and Securites Other than Mortgage-backed Securities [Member] | US Government Agencies Debt Securities [Member] | 3,295,000 | 30,000 | 0 | 3,325,000 |
US States and Political Subdivisions [Member] | 47,620,000 | 331,000 | 41,000 | 47,910,000 |
US Government-sponsored Enterprises Debt Securities [Member] | 294,223,000 | 1,289,000 | 48,000 | 295,464,000 |
| Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | 1,678,828,000 | 12,414,000 | 6,771,000 | 1,684,471,000 |
Mortgage-backed Securities, Issued by Private Enterprises [Member] | 312,973,000 | 0 | 8,533,000 | 304,440,000 |
Mortgage-backed Securities [Member] | 1,991,801,000 | 12,414,000 | 15,304,000 | 1,988,911,000 |
Other Debt Securities [Member] | 228,421,000 | 172,000 | 1,013,000 | 227,580,000 |
Major Types of Debt and Equity Securities [Domain] | 2,565,360,000 | 14,236,000 | 16,406,000 | 2,563,190,000 |
2006 | | Debt and Securites Other than Mortgage-backed Securities [Member] | US Government Agencies Debt Securities [Member] | 19,036,000 | 7,000 | 103,000 | 18,940,000 |
US States and Political Subdivisions [Member] | 38,833,000 | 125,000 | 178,000 | 38,780,000 |
US Government-sponsored Enterprises Debt Securities [Member] | 258,938,000 | 125,000 | 1,167,000 | 257,896,000 |
| Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | 1,626,206,000 | 2,982,000 | 30,808,000 | 1,598,380,000 |
Mortgage-backed Securities, Issued by Private Enterprises [Member] | 364,687,000 | 0 | 7,923,000 | 356,764,000 |
Mortgage-backed Securities [Member] | 1,990,893,000 | 2,982,000 | 38,731,000 | 1,955,144,000 |
Other Debt Securities [Member] | 333,131,000 | 101,000 | 6,115,000 | 327,117,000 |
Major Types of Debt and Equity Securities [Domain] | 2,640,831,000 | 3,340,000 | 46,294,000 | 2,597,877,000 |
2005 | | Debt and Securites Other than Mortgage-backed Securities [Member] | US Government Agencies Debt Securities [Member] | 4,455,000 | 17,000 | 37,000 | 4,435,000 |
US States and Political Subdivisions [Member] | 33,240,000 | 54,000 | 334,000 | 32,960,000 |
US Government-sponsored Enterprises Debt Securities [Member] | 96,103,000 | 142,000 | 569,000 | 95,676,000 |
| Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | 1,686,626,000 | 4,366,000 | 30,028,000 | 1,660,964,000 |
Mortgage-backed Securities, Issued by Private Enterprises [Member] | 427,019,000 | 0 | 8,131,000 | 418,888,000 |
Mortgage-backed Securities [Member] | 2,113,645,000 | 4,366,000 | 38,159,000 | 2,079,852,000 |
Other Debt Securities [Member] | 333,418,000 | 127,000 | 8,253,000 | 325,292,000 |
Major Types of Debt and Equity Securities [Domain] | 2,580,861,000 | 4,706,000 | 47,352,000 | 2,538,215,000 |