Securities (Tables)

12 Months Ended

Dec. 31, 2017

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
	December 31, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and   government agency   securities	$	99,535	$	—	$	2,263	$	97,272	$	56,751	$	—	$	1,923	$	54,828
Municipal obligations		245,997		1,135		3,346		243,786		253,228		113		11,186		242,155
Residential mortgage-backed  securities		1,729,989		5,611		20,387		1,715,213		1,620,191		10,592		19,428		1,611,355
Commercial mortgage-backed  securities		704,518		480		17,863		687,135		425,750		—		23,159		402,591
Collateralized mortgage   obligations		165,518		4		1,559		163,963		202,580		490		591		202,479
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	2,949,057	$	7,230	$	45,418	$	2,910,869	$	2,562,000	$	11,195	$	56,287	$	2,516,908

Amortized Cost and Fair Value of Securities Held to Maturity

Securities Held to Maturity
	December 31, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and   government agency   securities	$	50,000	$	—	$	289	$	49,711	$	50,000	$	—	$	44	$	49,956
Municipal obligations		723,094		8,323		4,245		727,172		648,093		2,147		20,175		630,065
Residential mortgage-backed securities		725,748		4,175		2,690		727,233		862,162		4,329		3,068		863,423
Commercial mortgage-backed securities		317,185		40		3,915		313,310		75,739		—		4,038		71,701
Collateralized mortgage   obligations		1,161,484		572		17,472		1,144,584		864,226		1,420		10,674		854,972
	$	2,977,511	$	13,110	$	28,611	$	2,962,010	$	2,500,220	$	7,896	$	37,999	$	2,470,117

Available for Sale [Member]

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

(in thousands)	Amortized Cost		Fair Value
Debt Securities Available for Sale
Due in one year or less	$	7,624	$	7,658
Due after one year through five years		40,743		41,083
Due after five years through ten years		1,226,635		1,208,735
Due after ten years		1,674,055		1,653,393
Total available for sale debt securities	$	2,949,057	$	2,910,869

Securities with Unrealized Losses

The details for securities classified as available for sale with unrealized losses as of December 31, 2017 follow.

Available for sale
	Losses < 12 Months				Losses 12 Months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government   agency securities	$	45,616	$	42	$	51,157	$	2,221	$	96,773	$	2,263
Municipal obligations		2,768		11		173,530		3,335		176,298		3,346
Residential mortgage-backed securities		461,835		4,195		898,099		16,192		1,359,934		20,387
Commercial mortgage-backed securities		203,618		995		411,046		16,868		614,664		17,863
Collateralized mortgage obligations		128,174		1,076		35,488		483		163,662		1,559
	$	842,011	$	6,319	$	1,569,320	$	39,099	$	2,411,331	$	45,418

The details for securities classified as available for sale with unrealized losses as of December 31, 2016 follow.

Available for sale
	Losses < 12 Months				Losses 12 Months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government   agency securities	$	54,788	$	1,923	$	—	$	—	$	54,788	$	1,923
Municipal obligations		228,588		11,186		—		—		228,588		11,186
Residential mortgage-backed securities		1,087,644		19,359		3,738		69		1,091,382		19,428
Commercial mortgage-backed securities		402,591		23,159		—		—		402,591		23,159
Collateralized mortgage obligations		83,701		591		—		—		83,701		591
	$	1,857,312	$	56,218	$	3,738	$	69	$	1,861,050	$	56,287

Held to Maturity [Member]

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

(in thousands)	Amortized Cost		Fair Value
Debt Securities Held to Maturity
Due in one year or less	$	10,686	$	10,695
Due after one year through five years		122,555		122,339
Due after five years through ten years		1,052,688		1,051,036
Due after ten years		1,791,582		1,777,940
Total held to maturity debt securities	$	2,977,511	$	2,962,010

Securities with Unrealized Losses

The details for securities classified as held to maturity with unrealized losses as of December 31, 2017 follow.

Securities Held to Maturity
	Losses < 12 Months				Losses 12 Months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government   agency securities	$	—	$	—	$	49,711	$	289	$	49,711	$	289
Municipal obligations		14,603		19		230,960		4,226		245,563		4,245
Residential mortgage-backed securities		8,815		99		230,277		2,591		239,092		2,690
Commercial mortgage-backed securities		174,882		744		72,499		3,171		247,381		3,915
Collateralized mortgage obligations		570,289		5,653		472,536		11,819		1,042,825		17,472
	$	768,589	$	6,515	$	1,055,983	$	22,096	$	1,824,572	$	28,611

The details for securities classified as held to maturity with unrealized losses as of December 31, 2016 follow.

Securities Held to Maturity
	Losses < 12 Months				Losses 12 Months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government   agency securities	$	49,956	$	44	$	—	$	—	$	49,956	$	44
Municipal obligations		494,470		19,706		11,750		469		506,220		20,175
Residential mortgage-backed securities		278,369		3,068		—		—		278,369		3,068
Commercial mortgage-backed securities		71,701		4,038		—		—		71,701		4,038
Collateralized mortgage obligations		618,739		7,296		115,375		3,378		734,114		10,674
	$	1,513,235	$	34,152	$	127,125	$	3,847	$	1,640,360	$	37,999