Securities, Available for Sale (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) Position	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Position	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,354,349		$ 1,354,349		$ 1,341,059
Unrealized gains	11,564		11,564		11,097
Unrealized losses	8,299		8,299		13,866
Estimated fair value	1,357,614		1,357,614		1,338,290
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	582,941		582,941		902,506
12 months or longer	189,144		189,144		5,831
Total	772,085		772,085		908,337
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(4,442)		(4,442)		(12,347)
12 months or longer	(3,857)		(3,857)		(1,519)
Total	$ (8,299)		$ (8,299)		$ (13,866)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	120		120		171
12 months or longer | Position	35		35		7
Total | Position	155		155		178
OTTI loss realized on equity investment	$ 0	$ 0	$ 1,300	$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	92,405		92,405
From one to five years	84,442		84,442
From five to ten years	179,854		179,854
After ten years	984,111		984,111
Amortized cost	1,340,812		1,340,812
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	92,429		92,429
From one to five years	84,598		84,598
From five to ten years	180,667		180,667
After ten years	980,181		980,181
Fair value	1,337,875		1,337,875
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	139,935		139,935		$ 175,135
Unrealized gains	27		27		78
Unrealized losses	544		544		805
Estimated fair value	139,418		139,418		174,408
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	45,209		45,209		119,363
12 months or longer	54,465		54,465		0
Total	99,674		99,674		119,363
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(49)		(49)		(805)
12 months or longer	(495)		(495)		0
Total	$ (544)		$ (544)		$ (805)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	3		3		10
12 months or longer | Position	5		5		0
Total | Position	8		8		10
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 42,880		$ 42,880		$ 47,053
Unrealized gains	127		127		153
Unrealized losses	88		88		480
Estimated fair value	42,919		42,919		46,726
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	14,720		14,720		31,873
12 months or longer	6,015		6,015		483
Total	20,735		20,735		32,356
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(39)		(39)		(478)
12 months or longer	(49)		(49)		(2)
Total	$ (88)		$ (88)		$ (480)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	24		24		55
12 months or longer | Position	8		8		1
Total | Position	32		32		56
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 181,600		$ 181,600		$ 277,524
12 months or longer	6,577		6,577		985
Total	188,177		188,177		278,509
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,176)		(1,176)		(2,668)
12 months or longer	(107)		(107)		(13)
Total	$ (1,283)		$ (1,283)		$ (2,681)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	42		42		49
12 months or longer | Position	5		5		4
Total | Position	47		47		53
Mortgage-Backed, Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 554,466		$ 554,466		$ 513,814
Unrealized gains	3,879		3,879		3,345
Unrealized losses	1,115		1,115		2,492
Estimated fair value	557,230		557,230		514,667
Mortgage-Backed, U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	26,760		26,760		14,955
Unrealized gains	404		404		411
Unrealized losses	168		168		189
Estimated fair value	26,996		26,996		15,177
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	339,415		339,415		473,746
12 months or longer	119,108		119,108		0
Total	458,523		458,523		473,746
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(3,175)		(3,175)		(8,396)
12 months or longer	(3,079)		(3,079)		0
Total	$ (6,254)		$ (6,254)		$ (8,396)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	50		50		57
12 months or longer | Position	16		16		0
Total | Position	66		66		57
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 523,682		$ 523,682		$ 513,431
Unrealized gains	626		626		532
Unrealized losses	5,592		5,592		7,688
Estimated fair value	518,716		518,716		506,275
Collateralized Mortgage Obligations, U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	53,089		53,089		60,822
Unrealized gains	169		169		184
Unrealized losses	662		662		708
Estimated fair value	52,596		52,596		60,298
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	13,537		13,537		15,849
Unrealized gains	6,332		6,332		6,394
Unrealized losses	130		130		1,504
Estimated fair value	19,739		19,739		20,739
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	1,997		1,997		0
12 months or longer	2,979		2,979		4,363
Total	4,976		4,976		4,363
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(3)		(3)		0
12 months or longer	(127)		(127)		(1,504)
Total	$ (130)		$ (130)		$ (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