Securities (Tables)

12 Months Ended

Dec. 31, 2018

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
	December 31, 2018								December 31, 2017
			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	$	74,339	$	—	$	2,633	$	71,706	$	99,535	$	—	$	2,263	$	97,272
Municipal obligations		246,713		360		6,646		240,427		245,997		1,135		3,346		243,786
Residential mortgage-backed  securities		1,468,912		4,284		29,794		1,443,402		1,729,989		5,611		20,387		1,715,213
Commercial mortgage-backed  securities		799,060		1,953		30,936		770,077		704,518		480		17,863		687,135
Collateralized mortgage   obligations		163,282		903		2,260		161,925		165,518		4		1,559		163,963
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	2,755,806	$	7,500	$	72,269	$	2,691,037	$	2,949,057	$	7,230	$	45,418	$	2,910,869

Amortized Cost and Fair Value of Securities Held to Maturity

Securities Held to Maturity
	December 31, 2018								December 31, 2017
			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	$	—	$	478	$	49,522	$	50,000	$	—	$	289	$	49,711
Municipal obligations		688,201		2,347		9,503		681,045		723,094		8,323		4,245		727,172
Residential mortgage-backed  securities		640,393		1,461		6,117		635,737		725,748		4,175		2,690		727,233
Commercial mortgage-backed  securities		357,175		376		10,882		346,669		317,185		40		3,915		313,310
Collateralized mortgage   obligations		1,243,778		1,598		22,493		1,222,883		1,161,484		572		17,472		1,144,584
	$	2,979,547	$	5,782	$	49,473	$	2,935,856	$	2,977,511	$	13,110	$	28,611	$	2,962,010

Proceeds from and Gross Losses on Sale of Securities

	Years Ended December 31,
(in thousands)	2018		2017		2016
Proceeds	$	455,162	$	213,877	$	173,215
Gross gains		—		—		1,965
Gross losses		25,480		—		211

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	$	1,862	$	1,868
Due after one year through five years		105,364		106,255
Due after five years through ten years		1,200,188		1,163,870
Due after ten years		1,448,392		1,419,044
Total available for sale debt securities	$	2,755,806	$	2,691,037

Securities with Unrealized Losses

The details for securities classified as available for sale with unrealized losses as of December 31, 2018 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	$	—	$	—	$	71,706	$	2,633	$	71,706	$	2,633
Municipal obligations		41,203		591		170,883		6,054		212,086		6,645
Residential mortgage-backed securities		305,090		2,485		762,826		27,309		1,067,916		29,794
Commercial mortgage-backed securities		96,226		1,851		570,485		29,085		666,711		30,936
Collateralized mortgage obligations		254		1		111,804		2,259		112,058		2,260
	$	442,773	$	4,928	$	1,687,704	$	67,340	$	2,130,477	$	72,268

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

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	$	18,654	$	18,676
Due after one year through five years		127,861		126,495
Due after five years through ten years		1,425,846		1,405,836
Due after ten years		1,407,186		1,384,849
Total held to maturity debt securities	$	2,979,547	$	2,935,856

Securities with Unrealized Losses

The details for securities classified as held to maturity with unrealized losses as of December 31, 2018 follow.

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	$	—	$	—	$	49,521	$	478	$	49,521	$	478
Municipal obligations		233,469		2,256		233,280		7,247		466,749		9,503
Residential mortgage-backed securities		90,730		123		235,251		5,994		325,981		6,117
Commercial mortgage-backed securities		—		—		305,419		10,882		305,419		10,882
Collateralized mortgage obligations		77,394		281		897,153		22,212		974,547		22,493
	$	401,593	$	2,660	$	1,720,624	$	46,813	$	2,122,217	$	49,473

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

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