Investment Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Carrying Amounts and Fair Values of Investment Securities

The carrying amounts and fair values of investment securities at December 31, 2017 and 2016 are summarized as follows: 

	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Fair Value
	(in thousands)
Held-to-maturity
Tax-exempt	$	255,050	$	4,514	$	(3,250	)	$	256,314
Available-for-sale
CDO	$	50	$	21,807	$	—		$	21,857
Commercial MBS issued by GSEs	113,069		46		(4,038		)	109,077
Corporate debt securities	105,044		261		(1,822		)	103,483
CRA investments	51,133		—		(517		)	50,616
Preferred stock	52,172		1,160		(136		)	53,196
Private label residential MBS	874,261		756		(6,493		)	868,524
Residential MBS issued by GSEs	1,719,188		810		(30,703		)	1,689,295
Tax-exempt	501,988		10,893		(1,971		)	510,910
Trust preferred securities	32,000		—		(3,383		)	28,617
U.S. government sponsored agency securities	64,000		—		(2,538		)	61,462
U.S. treasury securities	2,496		—		(14		)	2,482
Total AFS securities	$	3,515,401	$	35,733	$	(51,615	)	$	3,499,519

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Fair Value
	(in thousands)
Held-to-maturity
Tax-exempt	$	92,079	$	433	$	(546	)	$	91,966
Available-for-sale
CDO	$	50	$	13,440	$	—		$	13,490
Commercial MBS issued by GSEs	121,742		—		(3,950		)	117,792
Corporate debt securities	65,058		371		(1,285		)	64,144
CRA investments	37,627		—		(514		)	37,113
Preferred stock	96,071		833		(2,242		)	94,662
Private label residential MBS	440,272		182		(6,769		)	433,685
Residential MBS issued by GSEs	1,369,289		3,046		(17,130		)	1,355,205
Tax-exempt	409,693		8,477		(9,937		)	408,233
Trust preferred securities	32,000		—		(5,468		)	26,532
U.S. government sponsored agency securities	59,000		—		(2,978		)	56,022
U.S. treasury securities	2,496		6		—			2,502
Total AFS securities	$	2,633,298	$	26,355	$	(50,273	)	$	2,609,380
Securities measured at fair value
Residential MBS issued by GSEs								$	1,053

Unrealized Losses and Fair Value of Investment Securities in Continuous Unrealized Loss Position

Information pertaining to securities with gross unrealized losses at December 31, 2017 and 2016, aggregated by investment category and length of time that individual securities have been in a continuous loss position follows: 

	December 31, 2017
	Less Than Twelve Months				More Than Twelve Months				Total
	Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value
	(in thousands)
Held-to-maturity
Tax-exempt	$	3,250	$	107,921	$	—	$	—	$	3,250	$	107,921
Available-for-sale
Commercial MBS issued by GSEs	$	161	$	13,565	$	3,877	$	93,641	$	4,038	$	107,206
Corporate debt securities	1,398		78,602		424		19,576		1,822		98,178
CRA investments	—		—		517		50,616		517		50,616
Preferred stock	136		7,357		—		—		136		7,357
Private label residential MBS	3,115		480,885		3,378		188,710		6,493		669,595
Residential MBS issued by GSEs	13,875		999,478		16,828		523,270		30,703		1,522,748
Tax-exempt	17		6,159		1,954		69,674		1,971		75,833
Trust preferred securities	—		—		3,383		28,617		3,383		28,617
U.S. government sponsored agency securities	14		4,986		2,524		56,476		2,538		61,462
U.S. treasury securities	14		2,482		—		—		14		2,482
Total AFS securities	$	18,730	$	1,593,514	$	32,885	$	1,030,580	$	51,615	$	2,624,094

	December 31, 2016
	Less Than Twelve Months				More Than Twelve Months				Total
	Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value
	(in thousands)
Held-to-maturity
Tax-exempt	$	546	$	30,364	$	—	$	—	$	546	$	30,364
Available-for-sale
Commercial MBS issued by GSEs	$	3,950	$	117,792	$	—	$	—	$	3,950	$	117,792
Corporate debt securities	1,285		38,716		—		—		1,285		38,716
CRA investments	514		37,113		—		—		514		37,113
Preferred stock	2,188		63,151		54		1,471		2,242		64,622
Private label residential MBS	6,170		377,638		599		16,969		6,769		394,607
Residential MBS issued by GSEs	16,990		950,480		140		5,326		17,130		955,806
Tax-exempt	9,937		148,780		—		—		9,937		148,780
Trust preferred securities	—		—		5,468		26,532		5,468		26,532
U.S. government sponsored agency securities	2,978		56,022		—		—		2,978		56,022
Total AFS securities	$	44,012	$	1,789,692	$	6,261	$	50,298	$	50,273	$	1,839,990

Amortized Cost and Fair Value of Investment Securities by Contractual Maturities

The amortized cost and fair value of securities as of December 31, 2017, by contractual maturities, are shown below. MBS are shown separately as individual MBS are comprised of pools of loans with varying maturities. Therefore, these securities are listed separately in the maturity summary. 

	December 31, 2017
	Amortized Cost		Estimated Fair Value
	(in thousands)
Held-to-maturity
After one year through five years	$	11,300	$	11,377
After five years through ten years	14,979		14,860
After ten years	228,771		230,077
Total HTM securities	$	255,050	$	256,314
Available-for-sale
Due in one year or less	$	54,175	$	53,679
After one year through five years	16,992		17,464
After five years through ten years	257,495		256,147
After ten years	480,220		505,335
Mortgage-backed securities	2,706,519		2,666,894
Total AFS securities	$	3,515,401	$	3,499,519

Investment Securities by Credit Rating Type

The following tables summarize the carrying amount of the Company’s investment ratings position as of December 31, 2017 and 2016: 

	December 31, 2017
	AAA		Split-rated AAA/AA+		AA+ to AA-		A+ to A-		BBB+ to BBB-		BB+ and below		Unrated		Totals
	(in thousands)
Held-to-maturity
Tax-exempt	$	—	$	—	$	—	$	—	$	—	$	—	$	255,050	$	255,050
Available-for-sale
CDO	$	—	$	—	$	—	$	—	$	—	$	21,857	$	—	$	21,857
Commercial MBS issued by GSEs	—		109,077		—		—		—		—		—		109,077
Corporate debt securities	—		—		—		74,293		29,190		—		—		103,483
CRA investments	—		25,349		—		—		—		—		25,267		50,616
Preferred stock	—		—		—		10,388		23,822		4,104		14,882		53,196
Private label residential MBS	809,242		—		55,161		1,350		931		1,840		—		868,524
Residential MBS issued by GSEs	—		1,689,295		—		—		—		—		—		1,689,295
Tax-exempt	64,893		25,280		249,200		167,994		—		—		3,543		510,910
Trust preferred securities	—		—		—		—		28,617		—		—		28,617
U.S. government sponsored agency securities	—		61,462		—		—		—		—		—		61,462
U.S. treasury securities	—		2,482		—		—		—		—		—		2,482
Total AFS securities (1)	$	874,135	$	1,912,945	$	304,361	$	254,025	$	82,560	$	27,801	$	43,692	$	3,499,519

(1) Where ratings differ, the Company uses an average of the available ratings by S&P, Moody’s, and/or Fitch.

	December 31, 2016
	AAA		Split-rated AAA/AA+		AA+ to AA-		A+ to A-		BBB+ to BBB-		BB+ and below		Unrated		Totals
	(in thousands)
Held-to-maturity
Tax-exempt	$	—	$	—	$	—	$	—	$	—	$	—	$	92,079	$	92,079
Available-for-sale
CDO	$	—	$	—	$	—	$	—	$	—	$	13,490	$	—	$	13,490
Commercial MBS issued by GSEs	—		117,792		—		—		—		—		—		117,792
Corporate debt securities	—		—		5,429		38,715		20,000		—		—		64,144
CRA investments	—		—		—		—		—		—		37,113		37,113
Preferred stock	—		—		—		—		64,486		14,658		15,518		94,662
Private label residential MBS	399,013		—		29,921		2,117		2,634		—		—		433,685
Residential MBS issued by GSEs	—		1,355,205		—		—		—		—		—		1,355,205
Tax-exempt	80,862		—		268,249		59,122		—		—		—		408,233
Trust preferred securities	—		—		—		—		26,532		—		—		26,532
U.S. government sponsored agency securities	—		56,022		—		—		—		—		—		56,022
U.S. treasury securities	—		2,502		—		—		—		—		—		2,502
Total AFS securities (1)	$	479,875	$	1,531,521	$	303,599	$	99,954	$	113,652	$	28,148	$	52,631	$	2,609,380
Securities measured at fair value
Residential MBS issued by GSEs	$	—	$	1,053	$	—	$	—	$	—	$	—	$	—	$	1,053

(1) Where ratings differ, the Company uses an average of the available ratings by S&P, Moody’s, and/or Fitch.

Gross Gains and (Losses) on Sales of Investment Securities

The following table presents gross gains and losses on sales of investment securities: 

	Year Ended December 31,
	2017			2016			2015
	(in thousands)
Gross gains	$	3,204		$	2,115		$	1,144
Gross losses	(861		)	(1,056		)	(529		)
Net gains on sales of investment securities	$	2,343		$	1,059		$	615