Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Available-for-sale
Total available-for-sale securities, One Year or less	$ 13,902
Total available-for-sale securities, One to Five Years	78,016
Total available-for-sale securities, Five to Ten Years	81,752
Total available-for-sale securities, After Ten Years	69,535
Total available-for-sale securities, Mortgage-backed and Equity	750,065
Available-for-sale, Estimated Fair Value	993,270	1,021,244
Held-to-maturity
Total held-to-maturity securities, One Year or less, Fair value	2,728
Total held-to-maturity securities, One to Five Years	9,390
Total held-to-maturity securities, Five to Ten years	117,252
Total held-to-maturity securities, After Ten Years	356,202
Total held-to-maturity securities, Mortgage backed and Equity	139,055
Held-to-maturity securities, Fair value	624,627	639,273
Total securities, One Year or less	16,630
Total securities, One to Five Years	87,406
Total securities, Five to Ten Years, Fair value	199,004
Total securities, After Ten Years, Fair value	425,737
Total securities, Mortgage- backed and Equity	889,120
Total securities, Fair value	1,617,897
Other government agencies [Member]
Available-for-sale
Total available-for-sale securities, One Year or less
Total available-for-sale securities, One to Five Years	17,866
Total available-for-sale securities, Five to Ten Years	38,441
Total available-for-sale securities, After Ten Years	9,142
Total available-for-sale securities, Mortgage-backed and Equity
Available-for-sale, Estimated Fair Value	65,449	96,612
Residential mortgage-backed securities and collateralized mortgage obligations of government agencies [Member]
Available-for-sale
Total available-for-sale securities, One Year or less
Total available-for-sale securities, One to Five Years
Total available-for-sale securities, Five to Ten Years
Total available-for-sale securities, After Ten Years
Total available-for-sale securities, Mortgage-backed and Equity	738,942
Available-for-sale, Estimated Fair Value	738,942	732,210
Held-to-maturity
Total held-to-maturity securities, One Year or less, Fair value
Total held-to-maturity securities, One to Five Years
Total held-to-maturity securities, Five to Ten years
Total held-to-maturity securities, After Ten Years
Total held-to-maturity securities, Mortgage backed and Equity	138,743
Held-to-maturity securities, Fair value	138,743	159,213
Other residential collateralized mortgage obligations [Member]
Held-to-maturity
Total held-to-maturity securities, One Year or less, Fair value
Total held-to-maturity securities, One to Five Years
Total held-to-maturity securities, Five to Ten years
Total held-to-maturity securities, After Ten Years
Total held-to-maturity securities, Mortgage backed and Equity	312
Held-to-maturity securities, Fair value	312	361
Obligations of state and political subdivisions [Member]
Available-for-sale
Total available-for-sale securities, One Year or less	8,767
Total available-for-sale securities, One to Five Years	42,834
Total available-for-sale securities, Five to Ten Years	35,567
Total available-for-sale securities, After Ten Years	52,452
Total available-for-sale securities, Mortgage-backed and Equity
Available-for-sale, Estimated Fair Value	139,620	148,635
Held-to-maturity
Total held-to-maturity securities, One Year or less, Fair value	2,728
Total held-to-maturity securities, One to Five Years	9,390
Total held-to-maturity securities, Five to Ten years	117,252
Total held-to-maturity securities, After Ten Years	356,202
Total held-to-maturity securities, Mortgage backed and Equity
Held-to-maturity securities, Fair value	485,572	479,699
Corporate debt securities [Member]
Available-for-sale
Total available-for-sale securities, One Year or less	5,135
Total available-for-sale securities, One to Five Years	17,316
Total available-for-sale securities, Five to Ten Years	7,744
Total available-for-sale securities, After Ten Years	7,941
Total available-for-sale securities, Mortgage-backed and Equity
Available-for-sale, Estimated Fair Value	38,136	32,685
Equity securities [Member]
Available-for-sale
Total available-for-sale securities, One Year or less
Total available-for-sale securities, One to Five Years
Total available-for-sale securities, Five to Ten Years
Total available-for-sale securities, After Ten Years
Total available-for-sale securities, Mortgage-backed and Equity	11,123
Available-for-sale, Estimated Fair Value	$ 11,123	$ 11,102