Investment Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012
Debt securities available for sale:
Due in one year or less	$ 33,314
Due after one year through five years	40,715
Due after five years through ten years	11,098
Due after ten years	206,266
Total available for available for sale (amortized cost)	291,393
Mortgage-backed securities available for sale	5,106,367
Total	5,397,760
Debt securities available for sale:
Due in one year or less	33,367
Due after one year through five years	42,082
Due after five years through ten years	11,886
Due after ten years	187,859
Total available for available for sale (fair value)	275,194
Mortgage-backed securities available for sale	5,139,019
Total	5,414,213
Debt securities held to maturity:
Due in one year or less	30,983
Due after one year through five years	40,576
Due after five years through ten years	114,797
Due after ten years	12,906
Total available for held to maturity (amortized cost)	199,262
Mortgage-backed securities held to maturity	989,203
Total	1,188,465
Debt securities held to maturity:
Due in one year or less	31,166
Due after one year through five years	42,599
Due after five years through ten years	120,839
Due after ten years	13,003
Total available for held to maturity (fair value)	207,607
Mortgage-backed securities held to maturity	924,229
Total	$ 1,131,836