Securities Available for Sale (Tables)

6 Months Ended

Jun. 30, 2019

Debt Securities, Available-for-sale [Abstract]

Summary of Securities Available for Sale

The following is a summary of securities available for sale as of the dates indicated:



	At June 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
Debt securities:
U.S. Government agency and U.S. Government sponsored enterprises:
Collateralized mortgage obligations	$	842,576	$	5,443	$	(3,120	)	$	844,899
Mortgage-backed securities:
Residential	369,476		913		(3,213		)	367,176
Commercial	530,206		13,437		(2,712		)	540,931
Corporate securities	5,000		—		(1,120		)	3,880
Municipal securities	70,007		565		(555		)	70,017
Total investment securities available for sale	$	1,817,265	$	20,358	$	(10,720	)	$	1,826,903

	At December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(Dollars in thousands)
Debt securities:
U.S. Government agency and U.S. Government sponsored enterprises:
Collateralized mortgage obligations	$	914,710	$	1,541	$	(21,129	)	$	895,122
Mortgage-backed securities:
Residential	415,659		47		(13,101		)	402,605
Commercial	481,081		1,024		(12,979		)	469,126
Corporate securities	5,000		—		(1,174		)	3,826
Municipal securities	77,168		398		(1,980		)	75,586
Total investment securities available for sale	$	1,893,618	$	3,010	$	(50,363	)	$	1,846,265

Investments Classified by Contractual Maturity Date

The amortized cost and estimated fair value of investment securities at June 30, 2019, by contractual maturity, is presented in the table below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations, with or without call or prepayment penalties. Collateralized mortgage obligations and mortgage-backed securities are not due at a single maturity date and their total balances are shown separately.



	Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Available for sale:
Due within one year	$	750	$	752
Due after one year through five years	3,560		3,569
Due after five years through ten years	2,648		2,720
Due after ten years	68,049		66,856
U.S. Government agency and U.S. Government sponsored enterprises:
Collateralized mortgage obligations	842,576		844,899
Mortgage-backed securities:
Residential	369,476		367,176
Commercial	530,206		540,931
Total	$	1,817,265	$	1,826,903

Schedule of Unrealized Loss on Investments

The following tables show the Company’s investments’ gross unrealized losses and estimated fair values, aggregated by investment category and the length of time that the individual securities have been in a continuous unrealized loss position as of the dates indicated.



	As of June 30, 2019
	Less than 12 months					12 months or longer						Total
Description of Securities	Number of Securities	Fair Value		Gross Unrealized Losses		Number of Securities	Fair Value		Gross Unrealized Losses			Number of Securities	Fair Value		Gross Unrealized Losses
	(Dollars in thousands)
Collateralized mortgage obligations*	—	$	—	$	—	56	$	360,072	$	(3,120	)	56	$	360,072	$	(3,120	)
Mortgage-backed securities:
Residential*	—	—		—		37	309,942		(3,213		)	37	309,942		(3,213		)
Commercial*	—	—		—		11	147,737		(2,712		)	11	147,737		(2,712		)
Corporate securities	—	—		—		1	3,881		(1,120		)	1	3,881		(1,120		)
Municipal securities	—	—		—		3	17,608		(555		)	3	17,608		(555		)
Total	—	$	—	$	—	108	$	839,240	$	(10,720	)	108	$	839,240	$	(10,720	)

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* Investments in U.S. Government agency and U.S. Government sponsored enterprises



	As of December 31, 2018
	Less than 12 months						12 months or longer						Total
Description of Securities	Number of Securities	Fair Value		Gross Unrealized Losses			Number of Securities	Fair Value		Gross Unrealized Losses			Number of Securities	Fair Value		Gross Unrealized Losses
	(Dollars in thousands)
Collateralized mortgage obligations*	1	$	8,041	$	(28	)	93	$	700,095	$	(21,101	)	94	$	708,136	$	(21,129	)
Mortgage-backed securities:
Residential*	4	19,973		(37		)	45	363,334		(13,064		)	49	383,307		(13,101		)
Commercial*	3	38,494		(218		)	27	312,428		(12,761		)	30	350,922		(12,979		)
Corporate securities	—	—		—			1	3,826		(1,174		)	1	3,826		(1,174		)
Municipal securities	13	5,528		(83		)	32	42,444		(1,897		)	45	47,972		(1,980		)
Total	21	$	72,036	$	(366	)	198	$	1,422,127	$	(49,997	)	219	$	1,494,163	$	(50,363	)

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* Investments in U.S. Government agency and U.S. Government sponsored enterprises