Securities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,434,468	$ 1,349,416	[1]
Gross Unrealized Gains	23,187	46,486
Gross Unrealized Losses	23,201	2,562
Fair Value	1,434,454	1,393,340
Obligations of U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	585,539	570,871	[1]
Gross Unrealized Gains	9,625	22,909
Gross Unrealized Losses	6,853	2
Fair Value	588,311	593,778
Obligations of U.S. states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73,769	76,803	[1]
Gross Unrealized Gains	1,417	2,326
Gross Unrealized Losses	1,235	73
Fair Value	73,951	79,056
Residential Mortgage-backed securities U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	143,418	162,853	[1]
Gross Unrealized Gains	3,223	5,362
Gross Unrealized Losses	2,348	548
Fair Value	144,293	167,667
Residential Mortgage-backed securities U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	624,318	526,364	[1]
Gross Unrealized Gains	8,860	15,759
Gross Unrealized Losses	12,600	1,768
Fair Value	620,578	540,355
Residential Mortgage-backed securities Non-U.S. Government agencies or sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	385	4,457	[1]
Gross Unrealized Gains	9	40
Gross Unrealized Losses	0	143
Fair Value	394	4,354
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,005	5,009	[1]
Gross Unrealized Gains	53	87
Gross Unrealized Losses	113	13
Fair Value	4,945	5,083
Total debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,432,434	1,347,358	[1]
Gross Unrealized Gains	23,187	46,486
Gross Unrealized Losses	23,149	2,547
Fair Value	1,432,472	1,391,297
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,034	2,058	[1]
Gross Unrealized Gains	0	0
Gross Unrealized Losses	52	15
Fair Value	1,982	2,043
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,001	[1]
Gross Unrealized Gains		3
Gross Unrealized Losses		0
Fair Value		$ 1,004

[1] Net of other-than-temporary impairment losses recognized in earnings.