Securities (Tables)

9 Months Ended

Sep. 30, 2017

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
(in thousands)	September 30, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	75,019	$	29	$	1,606	$	73,442	$	56,751	$	—	$	1,923	$	54,828
Municipal obligations		246,805		534		4,661		242,678		253,228		113		11,186		242,155
Residential mortgage-backed securities		1,795,397		9,701		11,672		1,793,426		1,620,191		10,592		19,428		1,611,355
Commercial mortgage-backed securities		584,503		569		16,719		568,353		425,750		—		23,159		402,591
Collateralized mortgage obligations		174,119		114		354		173,879		202,580		490		591		202,479
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	2,879,343	$	10,947	$	35,012	$	2,855,278	$	2,562,000	$	11,195	$	56,287	$	2,516,908

Amortized Cost and Fair Value of Securities Held to Maturity

Securities Held to Maturity
(in thousands)	September 30, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	50,000	$	—	$	63	$	49,937	$	50,000	$	—	$	44	$	49,956
Municipal obligations		725,484		7,677		7,396		725,765		648,093		2,147		20,175		630,065
Residential mortgage-backed securities		760,158		8,896		776		768,278		862,162		4,329		3,068		863,423
Commercial mortgage-backed securities		75,688		—		2,592		73,096		75,739		—		4,038		71,701
Collateralized mortgage obligations		1,157,944		2,476		9,348		1,151,072		864,226		1,420		10,674		854,972
	$	2,769,274	$	19,049	$	20,175	$	2,768,148	$	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		Fair
Debt Securities Available for Sale	Cost		Value
Due in one year or less	$	5,392	$	5,425
Due after one year through five years		46,852		47,394
Due after five years through ten years		1,097,850		1,082,709
Due after ten years		1,729,249		1,719,750
Total available for sale debt securities	$	2,879,343	$	2,855,278

Securities with Unrealized Losses

Available for Sale
September 30, 2017	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	$	52,866		1,606	$	—	$	—	$	52,866	$	1,606
Municipal obligations		145,441		2,286		66,640		2,375		212,081		4,661
Residential mortgage-backed securities		1,255,266		11,514		5,360		158		1,260,626		11,672
Commercial mortgage-backed securities		465,596		15,366		30,151		1,353		495,747		16,719
Collateralized mortgage obligations		66,149		201		5,565		153		71,714		354
	$	1,985,318	$	30,973	$	107,716	$	4,039	$	2,093,034	$	35,012

Available for Sale
December 31, 2016	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

	Amortized		Fair
Debt Securities Held to Maturity	Cost		Value
Due in one year or less	$	10,081	$	10,123
Due after one year through five years		108,164		108,726
Due after five years through ten years		837,353		833,465
Due after ten years		1,813,676		1,815,834
Total held to maturity debt securities	$	2,769,274	$	2,768,148

Securities with Unrealized Losses

Held to maturity
September 30, 2017	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	$	49,938	$	63	$	—	$	—	$	49,938	$	63
Municipal obligations		275,874		2,975		98,976		4,421		374,850		7,396
Residential mortgage-backed securities		254,743		776		—		—		254,743		776
Commercial mortgage-backed securities		73,096		2,592		—		—		73,096		2,592
Collateralized mortgage obligations		559,859		3,852		232,697		5,496		792,556		9,348
	$	1,213,510	$	10,258	$	331,673	$	9,917	$	1,545,183	$	20,175

Held to maturity
December 31, 2016	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