Investment Securities (Tables)

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Value of Investment Securities

The majority of securities held are publicly traded, and the estimated fair values were obtained from an independent pricing service based upon market quotes.

	December 31, 2014
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss			Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Government agency	$	339,071	$	—	$	(8,228	)	$	330,843		10.55	%
Residential mortgage-backed securities		1,884,370		36,154		(3,028	)		1,917,496		61.12	%
CMOs / REMICs — residential		297,318		7,050		(277	)		304,091		9.69	%
Municipal bonds		557,823		22,463		(645	)		579,641		18.48	%
Other securities		5,000		87		—			5,087		0.16	%
Total	$	3,083,582	$	65,754	$	(12,178)		$	3,137,158		100.00	%

	December 31, 2013
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss			Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Government agency	$	350,378	$	22	$	(23,875	)	$	326,525		12.26	%
Residential mortgage-backed securities		1,391,631		13,100		(24,788	)		1,379,943		51.81	%
CMOs / REMICs — residential		361,573		6,576		(1,974	)		366,175		13.75	%
Municipal bonds		571,145		18,839		(3,893	)		586,091		22.00	%
Other securities		5,000		—		(92	)		4,908		0.18	%
Total	$	2,679,727	$	38,537	$	(54,622)		$	2,663,642		100.00	%

Summary of Continuous Unrealized Loss Position of Securities

The tables below show the Company’s investment securities’ gross unrealized losses and fair value by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2014, and 2013. Management has reviewed individual securities to determine whether a decline in fair value below the amortized cost basis is other-than-temporary.

	December 31, 2014
	Less Than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Available-for-sale:
Government agency	$	22,224	$	28	$	307,873	$	8,200	$	330,097	$	8,228
Residential mortgage-backed securities		19,636		4		145,681		3,024		165,317		3,028
CMOs /REMICs — residential		—		—		31,143		277		31,143		277
Municipal bonds		1,953		23		24,812		622		26,765		645
Other securities		—		—		—		—		—		—
Total	$	43,813	$	55	$	509,509	$	12,123	$	553,322	$	12,178

	December 31, 2013
	Less Than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Available-for-sale:
Government agency	$	267,936	$	20,514	$	38,563	$	3,361	$	306,499	$	23,875
Residential mortgage-backed securities		851,621		23,313		22,999		1,475		874,620		24,788
CMOs / REMICs — residential		104,322		1,780		17,747		194		122,069		1,974
Municipal bonds		47,116		3,359		10,338		534		57,454		3,893
Other securities		4,908		92		—		—		4,908		92
Total	$	1,275,903	$	49,058	$	89,647	$	5,564	$	1,365,550	$	54,622

Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

Mortgage-backed securities and CMO/REMICs are included in maturity categories based upon estimated prepayment speeds.

	December 31, 2014
	Amortized Cost		Fair Value
	(Dollars in thousands)
Available-for-sale:
Due in one year or less	$	156,040	$	159,389
Due after one year through five years		2,056,835		2,107,877
Due after five years through ten years		757,260		754,160
Due after ten years		113,447		115,732
Total	$	3,083,582	$	3,137,158