Securities, Available for Sale (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Position	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Position	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,363,616		$ 1,363,616		$ 1,341,059
Unrealized gains	10,518		10,518		11,097
Unrealized losses	8,613		8,613		13,866
Estimated fair value	1,365,521		1,365,521		1,338,290
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	799,017		799,017		902,506
12 months or longer	11,338		11,338		5,831
Total	810,355		810,355		908,337
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(8,364)		(8,364)		(12,347)
12 months or longer	(249)		(249)		(1,519)
Total	$ (8,613)		$ (8,613)		$ (13,866)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	153		153		171
12 months or longer | Position	8		8		7
Total | Position	161		161		178
OTTI loss realized on equity investment	$ 0	$ 0	$ 1,300	$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	63,613		63,613
From one to five years	136,121		136,121
From five to ten years	163,507		163,507
After ten years	986,838		986,838
Amortized cost	1,350,079		1,350,079
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	63,631		63,631
From one to five years	136,321		136,321
From five to ten years	164,061		164,061
After ten years	982,496		982,496
Fair value	1,346,509		1,346,509
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	159,999		159,999		$ 175,135
Unrealized gains	46		46		78
Unrealized losses	525		525		805
Estimated fair value	159,520		159,520		174,408
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	109,778		109,778		119,363
12 months or longer	0		0		0
Total	109,778		109,778		119,363
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(525)		(525)		(805)
12 months or longer	0		0		0
Total	$ (525)		$ (525)		$ (805)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	9		9		10
12 months or longer | Position	0		0		0
Total | Position	9		9		10
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 44,023		$ 44,023		$ 47,053
Unrealized gains	136		136		153
Unrealized losses	139		139		480
Estimated fair value	44,020		44,020		46,726
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	23,771		23,771		31,873
12 months or longer	1,052		1,052		483
Total	24,823		24,823		32,356
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(120)		(120)		(478)
12 months or longer	(19)		(19)		(2)
Total	$ (139)		$ (139)		$ (480)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	36		36		55
12 months or longer | Position	1		1		1
Total | Position	37		37		56
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 210,648		$ 210,648		$ 277,524
12 months or longer	963		963		985
Total	211,611		211,611		278,509
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,618)		(1,618)		(2,668)
12 months or longer	(13)		(13)		(13)
Total	$ (1,631)		$ (1,631)		$ (2,681)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	46		46		49
12 months or longer | Position	4		4		4
Total | Position	50		50		53
Mortgage-Backed, Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 544,616		$ 544,616		$ 513,814
Unrealized gains	3,503		3,503		3,345
Unrealized losses	1,414		1,414		2,492
Estimated fair value	546,705		546,705		514,667
Mortgage-Backed, U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	17,167		17,167		14,955
Unrealized gains	406		406		411
Unrealized losses	217		217		189
Estimated fair value	17,356		17,356		15,177
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	452,830		452,830		473,746
12 months or longer	6,347		6,347		0
Total	459,177		459,177		473,746
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(6,091)		(6,091)		(8,396)
12 months or longer	(88)		(88)		0
Total	$ (6,179)		$ (6,179)		$ (8,396)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	61		61		57
12 months or longer | Position	2		2		0
Total | Position	63		63		57
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 528,561		$ 528,561		$ 513,431
Unrealized gains	622		622		532
Unrealized losses	5,551		5,551		7,688
Estimated fair value	523,632		523,632		506,275
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	55,713		55,713		60,822
Unrealized gains	191		191		184
Unrealized losses	628		628		708
Estimated fair value	55,276		55,276		60,298
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	13,537		13,537		15,849
Unrealized gains	5,614		5,614		6,394
Unrealized losses	139		139		1,504
Estimated fair value	19,012		19,012		20,739
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	1,990		1,990		0
12 months or longer	2,976		2,976		4,363
Total	4,966		4,966		4,363
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(10)		(10)		0
12 months or longer	(129)		(129)		(1,504)
Total	$ (139)		$ (139)		$ (1,504)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	1		1		0
12 months or longer | Position	1		1		2
Total | Position	2		2		2