Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,384,804	$ 1,368,736
Gross Unrealized Gains	18,430	19,602
Gross Unrealized Losses	23,632	33,527
Fair Value	1,379,600	1,354,811
Obligations of U.S. Government sponsored entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	543,889	558,130
Gross Unrealized Gains	7,114	7,720
Gross Unrealized Losses	4,604	9,505
Fair Value	546,398	556,345
Obligations of U.S. states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	69,066	68,216
Gross Unrealized Gains	1,149	1,193
Gross Unrealized Losses	849	1,447
Fair Value	69,366	67,962
Residential Mortgage-backed securities U.S. Government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	140,583	147,766
Gross Unrealized Gains	2,631	2,554
Gross Unrealized Losses	2,244	3,642
Fair Value	140,970	146,678
Residential Mortgage-backed securities U.S. Government sponsored entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	626,993	587,843
Gross Unrealized Gains	7,531	8,122
Gross Unrealized Losses	15,499	18,493
Fair Value	619,026	577,472
Residential Mortgage-backed securities Non-U.S. Government agencies or sponsored entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	297	306
Gross Unrealized Gains	5	5
Gross Unrealized Losses	0	0
Fair Value	302	311
U.S. corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,500	5,000
Gross Unrealized Gains	0	8
Gross Unrealized Losses	375	375
Fair Value	2,125	4,633
Total debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,383,329	1,367,261
Gross Unrealized Gains	18,430	19,602
Gross Unrealized Losses	23,571	33,462
Fair Value	1,378,186	1,353,401
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,475	1,475
Gross Unrealized Gains	0	0
Gross Unrealized Losses	61	65
Fair Value	$ 1,414	$ 1,410