Investment Securities (Tables)

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Schedule of Amortized Cost and Fair Values of Investment Securities, with Gross Unrealized Gains and Losses

The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following:

	December 31, 2014
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	317,386	$	1,700	$	(3,533	)	$	315,553
Obligations of state and political obligations		86,513		3,679		(2	)		90,190
Mortgage-backed securities		1,741,917		16,882		(7,184	)		1,751,615
Other securities		1,460		35		—			1,495
Total securities available for sale	$	2,147,276	$	22,296	$	(10,719	)	$	2,158,853
Securities held to maturity:
U.S. Government-sponsored enterprise obligations	$	10,000	$	88	$	—		$	10,088
Obligations of state and political obligations		77,597		3,153		(145	)		80,605
Mortgage-backed securities		29,363		151		(726	)		28,788
Total securities held to maturity	$	116,960	$	3,392	$	(871	)	$	119,481
	December 31, 2013
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	406,092	$	1,382	$	(11,913	)	$	395,561
Obligations of state and political obligations		105,300		2,435		(256	)		107,479
Mortgage-backed securities		1,450,194		10,031		(27,947	)		1,432,278
Other securities		1,460		19		—			1,479
Total securities available for sale	$	1,963,046	$	13,867	$	(40,116	)	$	1,936,797
Securities held to maturity:
U.S. Government-sponsored enterprise obligations	$	34,478	$	484	$	—		$	34,962
Obligations of state and political obligations		84,290		1,463		(1,624	)		84,129
Mortgage-backed securities		35,341		258		(2,124	)		33,475
Total securities held to maturity	$	154,109	$	2,205	$	(3,748	)	$	152,566

Schedule of Exposure to Investment Security Issuers Exceed Ten Percentage of Shareholders' Equity

At December 31, 2014, the Company’s exposure to two investment security issuers individually exceeded 10% of shareholders’ equity:

(Dollars in thousands)	Amortized Cost		Market Value
Federal National Mortgage Association (Fannie Mae)	$	1,220,841	$	1,226,654
Federal Home Loan Mortgage Corporation (Freddie Mac)		707,592		706,514
	$	1,928,433	$	1,933,168

Schedule of Securities with Gross Unrealized Losses Aggregated by Investment Category

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

	December 31, 2014
	Less Than Twelve Months					Over Twelve Months					Total
	Gross			Estimated		Gross			Estimated		Gross			Estimated
	Unrealized			Fair		Unrealized			Fair		Unrealized			Fair
(Dollars in thousands)	Losses			Value		Losses			Value		Losses			Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	—		$	—	$	(3,533	)	$	240,498	$	(3,533	)	$	240,498
Obligations of state and political obligations		(2	)		185		—			—		(2	)		185
Mortgage-backed securities		(1,189	)		304,686		(5,995	)		294,549		(7,184	)		599,235
Total securities available for sale	$	(1,191	)	$	304,871	$	(9,528	)	$	535,047	$	(10,719	)	$	839,918
Securities held to maturity:
Obligations of state and political obligations	$	(9	)	$	2,287	$	(136	)	$	8,590	$	(145	)	$	10,877
Mortgage-backed securities		—			—		(726	)		20,812		(726	)		20,812
Total securities held to maturity	$	(9	)	$	2,287	$	(862	)	$	29,402	$	(871	)	$	31,689
	December 31, 2013
	Less Than Twelve Months					Over Twelve Months					Total
	Gross			Estimated		Gross			Estimated		Gross			Estimated
	Unrealized			Fair		Unrealized			Fair		Unrealized			Fair
(Dollars in thousands)	Losses			Value		Losses			Value		Losses			Value
Securities available for sale:
U.S. Government-sponsored enterprise obligations	$	(11,764	)	$	298,515	$	(149	)	$	5,515	$	(11,913	)	$	304,030
Obligations of state and political obligations		(30	)		2,415		(226	)		1,047		(256	)		3,462
Mortgage-backed securities		(23,749	)		864,899		(4,198	)		81,870		(27,947	)		946,769
Total securities available for sale	$	(35,543	)	$	1,165,829	$	(4,573	)	$	88,432	$	(40,116	)	$	1,254,261
Securities held to maturity:
Obligations of state and political obligations	$	(1,181	)	$	29,355	$	(443	)	$	6,240	$	(1,624	)	$	35,595
Mortgage-backed securities		(952	)		12,913		(1,172	)		11,616		(2,124	)		24,529
Total securities held to maturity	$	(2,133	)	$	42,268	$	(1,615	)	$	17,856	$	(3,748	)	$	60,124

Additional Information on Securities in a Continuous Loss Position

Additional information on securities that have been in a continuous loss position for over twelve months at December 31 is presented in the following table.

(Dollars in thousands)	2014		2013
Number of securities
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae		66		20
Issued by political subdivisions		5		5
		71		25
Amortized Cost Basis
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae	$	566,113	$	104,520
Issued by political subdivisions		8,727		7,956
	$	574,840	$	112,476
Unrealized Loss
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae	$	10,254	$	5,519
Issued by political subdivisions		136		669
	$	10,390	$	6,188

Schedule of Other-Than-Temporarily Impaired Investment Security Portion of Unrealized Loss Recognized in Other Comprehensive Income

The following table reflects activity during the years ended December 31, 2014, 2013, and 2012 related to credit losses on the other-than-temporarily impaired investment security where a portion of the unrealized loss was recognized in comprehensive income.

(Dollars in thousands)	2014			2013			2012
Balance at beginning of period	$	(1,273	)	$	(1,273	)	$	(1,273	)
Credit losses on securities not previously considered other-than-temporarily impaired		—			—			—
Credit losses on securities for which OTTI was previously recognized		—			—			—
Reduction for securities sold/settled during the period		1,273			—			—
Balance at end of period	$	—		$	(1,273	)	$	(1,273	)

Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Maturity

The amortized cost and estimated fair value of investment securities by maturity at December 31, 2014 are shown in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Weighted average yields are calculated on the basis of the yield to maturity based on the amortized cost of each security.

	Securities Available for Sale							Securities Held to Maturity
(Dollars in thousands)	Weighted Average Yield			Amortized Cost		Estimated Fair Value		Weighted Average Yield			Amortized Cost		Estimated Fair Value
Within one year or less		1.54	%	$	14,643	$	14,764		2.65	%	$	10,000	$	10,088
One through five years		1.73			241,231		241,796		2.78			13,858		14,191
After five through ten years		2.15			425,233		429,973		3.10			20,945		21,729
Over ten years		2.20			1,466,169		1,472,320		2.86			72,157		73,473
		2.13	%	$	2,147,276	$	2,158,853		2.87	%	$	116,960	$	119,481

Schedule of Realized Gains and Losses from Sale of Securities Classified as Available for Sale

The following is a summary of realized gains and losses from the sale of securities classified as available for sale. Gains or losses on securities sold are recorded on the trade date, using the specific identification method.

	Years Ended December 31
(Dollars in thousands)	2014			2013			2012
Realized gains	$	863		$	2,387		$	3,754
Realized losses		(92	)		(110	)		(15	)
	$	771		$	2,277		$	3,739

Schedule of Securities in Other Assets on Company's Consolidated Balance Sheets

The Company included the following securities in “Other assets” on the consolidated balance sheets at December 31:

(Dollars in thousands)	2014		2013
Federal Home Loan Bank (FHLB) stock	$	38,476	$	24,369
Federal Reserve Bank (FRB) stock		34,348		28,098
Other investments		1,306		1,306
	$	74,130	$	53,773