Investment Securities (Tables)

12 Months Ended

Dec. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Schedule of Amortized Cost and Fair Values of Investment Securities

The following tables present the amortized cost and estimated fair values of investment securities, which were all classified as available for sale, as of December 31:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
2016
U.S. Government sponsored agency securities	$	132	$	2	$	—		$	134
State and municipal securities	405,274		2,043		(15,676		)	391,641
Corporate debt securities	112,016		1,978		(4,585		)	109,409
Collateralized mortgage obligations	604,095		1,943		(12,178		)	593,860
Mortgage-backed securities	1,353,292		6,546		(17,437		)	1,342,401
Auction rate securities	107,215		—		(9,959		)	97,256
Total debt securities	2,582,024		12,512		(59,835		)	2,534,701
Equity securities	12,231		12,295		—			24,526
Total	$	2,594,255	$	24,807	$	(59,835	)	$	2,559,227
2015
U.S. Government sponsored agency securities	$	25,154	$	35	$	(53	)	$	25,136
State and municipal securities	256,746		6,019		—			262,765
Corporate debt securities	100,336		2,695		(6,076		)	96,955
Collateralized mortgage obligations	835,439		3,042		(16,972		)	821,509
Mortgage-backed securities	1,154,935		10,104		(6,204		)	1,158,835
Auction rate securities	106,772		—		(8,713		)	98,059
Total debt securities	2,479,382		21,895		(38,018		)	2,463,259
Equity securities	14,677		6,845		(8		)	21,514
Total	$	2,494,059	$	28,740	$	(38,026	)	$	2,484,773

Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities

The amortized cost and estimated fair values of debt securities as of December 31, 2016, by contractual maturity, are shown in the following table. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less	$	54,727	$	55,027
Due from one year to five years	28,720		29,342
Due from five years to ten years	95,658		96,933
Due after ten years	445,532		417,138
	624,637		598,440
Collateralized mortgage obligations (1)	604,095		593,860
Mortgage-backed securities (1)	1,353,292		1,342,401
Total debt securities	$	2,582,024	$	2,534,701

Summary of Gains and Losses from Equity and Debt Securities, and Losses Recognized from Other-than-Temporary Impairment

The following table presents information related to gross gains and losses on the sales of equity and debt securities, and losses recognized for other-than-temporary impairment of investments:

	Gross Realized Gains		Gross Realized Losses			Other- than- temporary Impairment Losses			Net Gains
	(in thousands)
2016:
Equity securities	$	2,005	$	(10	)	$	—		$	1,995
Debt securities	581		(26		)	—			555
Total	$	2,586	$	(36	)	$	—		$	2,550
2015:
Equity securities	$	6,496	$	(1	)	$	—		$	6,495
Debt securities	2,571		—			—			2,571
Total	$	9,067	$	(1	)	$	—		$	9,066
2014:
Equity securities	$	335	$	—		$	(12	)	$	323
Debt securities	2,058		(322		)	(18		)	1,718
Total	$	2,393	$	(322	)	$	(30	)	$	2,041

Summary Of Other Than Temporary Impairment Charges Recorded In Statement Of Operations

There were no other-than-temporary impairment charges in 2016 or 2015. In 2014, there were $30,000 of other-than-temporary impairment charges, consisting of $12,000 of impairment charges on equity securities and $18,000 of charges on pooled trust preferred securities.

Summary of Cumulative Other-than-Temporary Impairment Charges Recognized in Earnings for Pooled Trust Preferred Securities Held

The following table presents a summary of the cumulative credit related other-than-temporary impairment charges, recognized as components of earnings, for debt securities held by the Corporation at December 31:

	2016			2015			2014
	(in thousands)
Balance of cumulative credit losses on debt securities, beginning of year	$	(11,510	)	$	(16,242	)	$	(20,691	)
Additions for credit losses recorded which were not previously recognized as components of earnings	—			—			(18		)
Reductions for securities sold during the period	—			4,730			4,460
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	—			2			7
Balance of cumulative credit losses on debt securities, end of year	$	(11,510	)	$	(11,510	)	$	(16,242	)

Gross Unrealized Losses and Fair Values of Investments by Category and Length of Time in Continuous Unrealized Loss Position

The following table presents the gross unrealized losses and estimated fair values of investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of December 31, 2016. There were no gross unrealized losses on equity securities as of December 31, 2016.

	Less Than 12 months					12 Months or Longer					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
	(in thousands)
State and municipal securities	$	247,509	$	(15,676	)	$	—	$	—		$	247,509	$	(15,676	)
Corporate debt securities	11,922		(110		)	34,629		(4,475		)	46,551		(4,585		)
Collateralized mortgage obligations	166,905		(3,899		)	258,237		(8,279		)	425,142		(12,178		)
Mortgage-backed securities	1,137,510		(17,437		)	—		—			1,137,510		(17,437		)
Auction rate securities	—		—			97,256		(9,959		)	97,256		(9,959		)
Total debt securities	1,563,846		(37,122		)	390,122		(22,713		)	1,953,968		(59,835		)

For comparative purposes, the following table presents gross unrealized losses and the estimated fair value of investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2015.

	Less Than 12 months					12 Months or Longer					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
	(in thousands)
U.S. Government sponsored agency securities	$	9,957	$	(53	)	$	—	$	—		$	9,957	$	(53	)
Corporate debt securities	12,892		(97		)	33,036		(5,979		)	45,928		(6,076		)
Collateralized mortgage obligations	166,007		(1,467		)	467,778		(15,505		)	633,785		(16,972		)
Mortgage-backed securities	611,920		(4,783		)	63,818		(1,421		)	675,738		(6,204		)
Auction rate securities	—		—			98,059		(8,713		)	98,059		(8,713		)
Total debt securities	800,776		(6,400		)	662,691		(31,618		)	1,463,467		(38,018		)
Equity securities	—		—			14		(8		)	14		(8		)
Total	$	800,776	$	(6,400	)	$	662,705	$	(31,626	)	$	1,463,481	$	(38,026	)

Summary of Amortized Cost and Fair Values of Corporate Debt Securities

The majority of the Corporation’s available for sale corporate debt securities are issued by financial institutions. The following table presents the amortized cost and estimated fair values of corporate debt securities as of December 31:

	2016				2015
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Single-issuer trust preferred securities	$	43,746	$	39,829	$	44,648	$	39,106
Subordinated debt	46,231		46,723		39,610		40,779
Senior debt	18,037		18,433		12,043		12,329
Pooled trust preferred securities	—		422		—		706
Corporate debt securities issued by financial institutions	108,014		105,407		96,301		92,920
Other corporate debt securities	4,002		4,002		4,035		4,035
Available for sale corporate debt securities	$	112,016	$	109,409	$	100,336	$	96,955