Securities (Tables)

3 Months Ended

Mar. 31, 2018

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
(in thousands)	March 31, 2018								December 31, 2017
			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	$	97,431		—		3,547		93,884	$	99,535	$	—	$	2,263	$	97,272
Municipal obligations		245,164		211		8,084		237,291		245,997		1,135		3,346		243,786
Residential mortgage-backed securities		1,787,382		3,552		47,391		1,743,543		1,729,989		5,611		20,387		1,715,213
Commercial mortgage-backed securities		715,360		—		35,088		680,272		704,518		480		17,863		687,135
Collateralized mortgage obligations		158,114		—		2,956		155,158		165,518		4		1,559		163,963
Corporate debt securities		5,500		—		—		5,500		3,500		—		—		3,500
	$	3,008,951	$	3,763	$	97,066	$	2,915,648	$	2,949,057	$	7,230	$	45,418	$	2,910,869

Amortized Cost and Fair Value of Securities Held to Maturity

Securities Held to Maturity
(in thousands)	March 31, 2018								December 31, 2017
			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		—		576		49,424	$	50,000	$	—	$	289	$	49,711
Municipal obligations		707,581		1,315		13,453		695,443		723,094		8,323		4,245		727,172
Residential mortgage-backed securities		695,655		721		10,624		685,752		725,748		4,175		2,690		727,233
Commercial mortgage-backed securities		316,966		—		11,400		305,566		317,185		40		3,915		313,310
Collateralized mortgage obligations		1,244,226		391		28,507		1,216,110		1,161,484		572		17,472		1,144,584
	$	3,014,428	$	2,427	$	64,560	$	2,952,295	$	2,977,511	$	13,110	$	28,611	$	2,962,010

Available for Sale [Member]

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

Debt Securities Available for Sale	Amortized		Fair
(in thousands)	Cost		Value
Due in one year or less	$	7,388	$	7,408
Due after one year through five years		45,623		45,740
Due after five years through ten years		1,249,127		1,202,997
Due after ten years		1,706,813		1,659,503
Total available for sale debt securities	$	3,008,951	$	2,915,648

Securities with Unrealized Losses

Available for Sale
March 31, 2018	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	$	43,521		1,214		50,362		2,333	$	93,883	$	3,547
Municipal obligations		54,330		948		169,119		7,136		223,449		8,084
Residential mortgage-backed securities		654,990		14,667		850,853		32,724		1,505,843		47,391
Commercial mortgage-backed securities		279,631		8,091		400,641		26,997		680,272		35,088
Collateralized mortgage obligations		122,186		2,324		32,972		632		155,158		2,956
	$	1,154,658	$	27,244	$	1,503,947	$	69,822	$	2,658,605	$	97,066

Available for Sale
December 31, 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	$	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

Debt Securities Held to Maturity	Amortized		Fair
(in thousands)	Cost		Value
Due in one year or less	$	4,190	$	4,205
Due after one year through five years		132,047		131,197
Due after five years through ten years		1,478,419		1,446,343
Due after ten years		1,399,772		1,370,550
Total held to maturity securities	$	3,014,428	$	2,952,295

Securities with Unrealized Losses

Held to maturity
March 31, 2018	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	$	—		—		49,424		576	$	49,424	$	576
Municipal obligations		341,011		4,530		221,438		8,923		562,449		13,453
Residential mortgage-backed securities		403,985		4,090		224,200		6,534		628,185		10,624
Commercial mortgage-backed securities		234,468		6,845		71,098		4,555		305,566		11,400
Collateralized mortgage obligations		672,660		12,567		441,866		15,940		1,114,526		28,507
	$	1,652,124	$	28,032	$	1,008,026	$	36,528	$	2,660,150	$	64,560

Held to maturity
December 31, 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	$	—	$	—	$	49,711	$	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