Securities (Tables)

6 Months Ended

Jun. 30, 2018

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
(in thousands)	June 30, 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	$	95,469		—		4,484		90,985	$	99,535	$	—	$	2,263	$	97,272
Municipal obligations		244,365		165		8,520		236,010		245,997		1,135		3,346		243,786
Residential mortgage-backed securities		1,826,589		2,609		54,327		1,774,871		1,729,989		5,611		20,387		1,715,213
Commercial mortgage-backed securities		770,769		153		41,390		729,532		704,518		480		17,863		687,135
Collateralized mortgage obligations		150,928		—		4,153		146,775		165,518		4		1,559		163,963
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	3,091,620	$	2,927	$	112,874	$	2,981,673	$	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)	June 30, 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		—		668		49,332	$	50,000	$	—	$	289	$	49,711
Municipal obligations		704,082		953		14,166		690,869		723,094		8,323		4,245		727,172
Residential mortgage-backed securities		665,846		194		14,730		651,310		725,748		4,175		2,690		727,233
Commercial mortgage-backed securities		357,680		153		14,581		343,252		317,185		40		3,915		313,310
Collateralized mortgage obligations		1,354,592		18		34,904		1,319,706		1,161,484		572		17,472		1,144,584
	$	3,132,200	$	1,318	$	79,049	$	3,054,469	$	2,977,511	$	13,110	$	28,611	$	2,962,010

Available for Sale Securities [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	$	5,073	$	5,088
Due after one year through five years		57,191		57,118
Due after five years through ten years		1,279,427		1,225,729
Due after ten years		1,749,929		1,693,738
Total available for sale debt securities	$	3,091,620	$	2,981,673

Securities with Unrealized Losses

Available for Sale
June 30, 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	$	42,423	$	1,812	$	48,562	$	2,672	$	90,985	$	4,484
Municipal obligations		54,121		984		168,133		7,536		222,254		8,520
Residential mortgage-backed securities		559,924		8,483		1,066,016		45,844		1,625,940		54,327
Commercial mortgage-backed securities		291,635		10,839		396,809		30,551		688,444		41,390
Collateralized mortgage obligations		115,891		3,007		30,884		1,146		146,775		4,153
	$	1,063,994	$	25,125	$	1,710,404	$	87,749	$	2,774,398	$	112,874

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 Securities [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	$	17,258	$	17,413
Due after one year through five years		137,093		135,198
Due after five years through ten years		1,474,871		1,436,090
Due after ten years		1,502,978		1,465,768
Total held to maturity securities	$	3,132,200	$	3,054,469

Securities with Unrealized Losses

Held to maturity
June 30, 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	$	—	$	—	$	49,332	$	668	$	49,332	$	668
Municipal obligations		364,751		5,081		220,575		9,085		585,326		14,166
Residential mortgage-backed securities		383,695		7,189		211,897		7,541		595,592		14,730
Commercial mortgage-backed securities		232,031		9,079		70,133		5,502		302,164		14,581
Collateralized mortgage obligations		592,423		8,113		677,684		26,791		1,270,107		34,904
	$	1,572,900	$	29,462	$	1,229,621	$	49,587	$	2,802,521	$	79,049

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