Securities (Tables)

6 Months Ended

Jun. 30, 2017

Gain (Loss) on Investments [Line Items]

Amortized Cost and Fair Value of Securities Available for Sale

Securities Available for Sale
(in thousands)	June 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	$	76,146	$	—	$	1,306	$	74,840	$	56,751	$	—	$	1,923	$	54,828
Municipal obligations		250,598		499		5,941		245,156		253,228		113		11,186		242,155
Residential mortgage-backed securities		1,860,644		9,765		16,310		1,854,099		1,620,191		10,592		19,428		1,611,355
Commercial mortgage-backed securities		449,912		463		17,277		433,098		425,750		—		23,159		402,591
Collateralized mortgage obligations		183,987		254		552		183,689		202,580		490		591		202,479
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	2,824,787	$	10,981	$	41,386	$	2,794,382	$	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)	June 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	$	—	$	64	$	49,936	$	50,000	$	—	$	44	$	49,956
Municipal obligations		730,599		7,205		9,614		728,190		648,093		2,147		20,175		630,065
Residential mortgage-backed securities		796,190		7,402		1,315		802,277		862,162		4,329		3,068		863,423
Commercial mortgage-backed securities		75,705		—		2,637		73,068		75,739		—		4,038		71,701
Collateralized mortgage obligations		1,221,960		1,690		10,592		1,213,058		864,226		1,420		10,674		854,972
	$	2,874,454	$	16,297	$	24,222	$	2,866,529	$	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

Debt Securities Available for Sale	Amortized		Fair
(in thousands)	Cost		Value
Due in one year or less	$	7,945	$	7,970
Due after one year through five years		38,273		38,767
Due after five years through ten years		997,109		980,311
Due after ten years		1,781,460		1,767,334
Total available for sale debt securities	$	2,824,787	$	2,794,382

Securities with Unrealized Losses

Available for Sale
June 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	$	74,308		1,306	$	—	$	—	$	74,308	$	1,306
Municipal obligations		213,557		5,941		—		—		213,557		5,941
Residential mortgage-backed securities		1,315,878		16,245		2,539		65		1,318,417		16,310
Commercial mortgage-backed securities		407,937		17,277		—		—		407,937		17,277
Collateralized mortgage obligations		74,282		552		—		—		74,282		552
Equity securities		—		—		—		—		—		—
	$	2,085,962	$	41,321	$	2,539	$	65	$	2,088,501	$	41,386

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
Corporate debt securities		—		—		—		—		—
	$	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	$	9,995	$	10,058
Due after one year through five years		108,634		109,069
Due after five years through ten years		851,644		845,017
Due after ten years		1,904,181		1,902,385
Total held to maturity securities	$	2,874,454	$	2,866,529

Securities with Unrealized Losses

Held to maturity
June 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	$	49,936	$	64	$	—	$	—	$	49,936	$	64
Municipal obligations		432,877		9,311		7,204		303		440,081		9,614
Residential mortgage-backed securities		268,110		1,315		—		—		268,110		1,315
Commercial mortgage-backed securities		73,068		2,637		—		—		73,068		2,637
Collateralized mortgage obligations		842,667		7,113		134,129		3,479		976,796		10,592
	$	1,666,658	$	20,440	$	141,333	$	3,782	$	1,807,991	$	24,222

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