Investments (Details 1) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Amortized costs and estimated fair values of pledged investment securities, available-for-sale
Amortized Cost	$ 851,746	$ 979,870
Available-for-sale, at fair value	869,268	991,438
Federal Home Loan Bank Advances [Member]
Amortized costs and estimated fair values of pledged investment securities, available-for-sale
Amortized Cost	764,161	877,766
Available-for-sale, at fair value	781,921	889,888
Federal Reserve Bank Advances [Member]
Amortized costs and estimated fair values of pledged investment securities, available-for-sale
Amortized Cost	19,942	35,056
Available-for-sale, at fair value	18,843	34,256
Non government corresponding bank securities [Member]
Amortized costs and estimated fair values of pledged investment securities, available-for-sale
Amortized Cost	39,992	37,979
Available-for-sale, at fair value	39,992	37,989
US Government Agencies Debt Securities [Member]
Amortized costs and estimated fair values of pledged investment securities, available-for-sale
Amortized Cost	27,651	29,069
Available-for-sale, at fair value	$ 28,512	$ 29,305