Investment Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Gains and Losses and Approximate Fair Values of Securities Available for Sale

The amortized cost, gross unrealized gains and losses and approximate fair values of available for sale debt securities are as follows:

	Amortized Cost		Unrealized				Fair Value
March 31, 2018			Gains		Losses
	(Dollars in thousands)
Available for sale debt securities:
U.S. Government agencies and sponsored enterprises obligations	$	91,364	$	30	$	1,384	$	90,010
U.S. Government agencies and sponsored enterprises mortgage-backed securities	611,868		187		15,619		596,436
State and municipal obligations	26,260		99		1,323		25,036
Asset-backed securities	670,439		1,388		218		671,609
Corporate bonds and other debt securities	787,471		15,625		5,617		797,479
Total available for sale debt securities	$	2,187,402	$	17,329	$	24,161	$	2,180,570
	Amortized Cost		Unrealized				Fair Value
December 31, 2017			Gains		Losses
	(Dollars in thousands)
Available for sale debt securities: (1)
U.S. Government agencies and sponsored enterprises obligations	$	43,471	$	38	$	671	$	42,838
U.S. Government agencies and sponsored enterprises mortgage-backed securities	600,310		1,716		6,789		595,237
State and municipal obligations	26,766		125		719		26,172
Asset-backed securities	608,340		2,306		100		610,546
Corporate bonds and other debt securities	738,994		18,222		1,313		755,903
Total available for sale debt securities	$	2,017,881	$	22,407	$	9,592	$	2,030,696

(1) To allow for improved comparability, prior year presentation has been modified to remove preferred stock and other equity securities in connection with the adoption of ASU 2016-01.

Schedule of Amortized Cost and Estimated Fair Value of Securities Available for Sale

The amortized cost and estimated fair value of available for sale debt securities, by contractual maturity, are as follows:

March 31, 2018	Amortized Cost		Fair Value
	(Dollars in thousands)
Available for sale debt securities:
Due in one year or less	$	57,851	$	57,857
Due after one year through five years	303,216		303,061
Due after five years through ten years	133,064		131,885
Due after ten years	319,600		329,712
U.S. Government agencies and sponsored enterprises obligations, mortgage-backed securities and asset-backed securities	1,373,671		1,358,055
Total available for sale debt securities	$	2,187,402	$	2,180,570

Summary of Estimated Fair Values and Gross Unrealized Losses on Investment Securities Available for Sale

The following tables present the estimated fair values and gross unrealized losses on available for sale debt securities, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position as of the periods presented:

	Less than 12 Months				12 Months or More				Total
March 31, 2018	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
	(Dollars in thousands)
Available for sale debt securities:
U.S. Government agencies and sponsored enterprises obligations	$	54,803	$	945	$	6,104	$	439	$	60,907	$	1,384
U.S. Government agencies and sponsored enterprises mortgage-backed securities	396,538		7,581		167,087		8,038		563,625		15,619
State and municipal obligations	186		7		22,707		1,316		22,893		1,323
Asset-backed securities	115,856		218		—		—		115,856		218
Corporate bonds and other debt securities	357,248		5,356		10,642		261		367,890		5,617
Total available for sale debt securities	$	924,631	$	14,107	$	206,540	$	10,054	$	1,131,171	$	24,161

	Less than 12 Months				12 Months or More				Total
December 31, 2017	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
	(Dollars in thousands)
Available for sale debt securities: (1)
U.S. Government agencies and sponsored enterprises obligations	$	31,518	$	268	$	7,157	$	403	$	38,675	$	671
U.S. Government agencies and sponsored enterprises mortgage-backed securities	207,735		1,836		175,810		4,953		383,545		6,789
State and municipal obligations	192		2		23,813		717		24,005		719
Asset-backed securities	36,542		100		—		—		36,542		100
Corporate bonds and other debt securities	186,052		1,240		10,842		73		196,894		1,313
Total available for sale debt securities	$	462,039	$	3,446	$	217,622	$	6,146	$	679,661	$	9,592

(1) To allow for improved comparability, prior year presentation has been modified to remove preferred stock and other equity securities in connection with the adoption of ASU 2016-01.

Summary of Gross Realized Gains and Losses on Sale of Securities Available for Sale

Gross realized gains and losses on the sale of available for sale debt securities are shown below. The cost of securities sold is based on the specific identification method.

	Three Months Ended March 31,
	2018			2017
	(Dollars in thousands)
Gross realized gains	$	1		$	325
Gross realized losses	(6		)	—
Net realized gains (losses)	$	(5	)	$	325