Investment Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Schedule of Amortized Cost and Fair Values of Investment Securities

The following table presents the amortized cost and estimated fair values of investment securities, which were all classified as available for sale:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
September 30, 2017
U.S. Government sponsored agency securities	$	5,961	$	54	$	—		$	6,015
State and municipal securities	415,313		4,005		(5,405		)	413,913
Corporate debt securities	92,355		2,578		(1,956		)	92,977
Collateralized mortgage obligations	601,845		1,380		(9,547		)	593,678
Residential mortgage-backed securities	1,184,797		5,850		(8,561		)	1,182,086
Commercial mortgage-backed securities	161,960		299		(627		)	161,632
Auction rate securities	107,410		—		(9,254		)	98,156
Total debt securities	2,569,641		14,166		(35,350		)	2,548,457
Equity securities	6,560		6,499		—			13,059
Total	$	2,576,201	$	20,665	$	(35,350	)	$	2,561,516

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
December 31, 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
Residential mortgage-backed securities	1,328,192		6,546		(16,900		)	1,317,838
Commercial mortgage-backed securities	25,100		—		(537		)	24,563
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

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 September 30, 2017, by contractual maturity, are shown in the following table. Actual maturities may differ from contractual maturities as certain investment securities are subject to call or prepayment with or without call or prepayment penalties.

		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less		$	23,940	$	24,118
Due from one year to five years		30,708		31,196
Due from five years to ten years		114,114		115,336
Due after ten years		452,277		440,411
		621,039		611,061
Residential mortgage-backed securities		1,184,797		1,182,086
Commercial mortgage-backed securities		161,960		161,632
Collateralized mortgage obligations		601,845		593,678
Total debt securities		$	2,569,641	$	2,548,457

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 the gross realized gains and losses on the sales of equity and debt securities:

	Gross Realized Gains		Gross Realized Losses			Net Gains (Losses)
Three months ended September 30, 2017	(in thousands)
Equity securities	$	4,817	$	—		$	4,817
Debt securities	12		(232		)	(220		)
Total	$	4,829	$	(232	)	$	4,597
Three months ended September 30, 2016
Equity securities	$	2	$	—		$	2
Debt securities	—		—			—
Total	$	2	$	—		$	2
Nine months ended September 30, 2017
Equity securities	$	7,167	$	—		$	7,167
Debt securities	218		(246		)	(28		)
Total	$	7,385	$	(246	)	$	7,139
Nine months ended September 30, 2016
Equity securities	$	739	$	(10	)	$	729
Debt securities	322		(26		)	296
Total	$	1,061	$	(36	)	$	1,025

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, at September 30, 2017 and 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
September 30, 2017	(in thousands)
State and municipal securities	$	121,527	$	(1,930	)	$	87,466	$	(3,475	)	$	208,993	$	(5,405	)
Corporate debt securities	3,570		(16		)	31,533		(1,940		)	35,103		(1,956		)
Collateralized mortgage obligations	85,335		(837		)	301,009		(8,710		)	386,344		(9,547		)
Residential mortgage-backed securities	796,019		(8,359		)	5,513		(202		)	801,532		(8,561		)
Commercial mortgage-backed securities	87,260		(627		)	—		—			87,260		(627		)
Auction rate securities	—		—			98,156		(9,254		)	98,156		(9,254		)
Total debt securities	$	1,093,711	$	(11,769	)	$	523,677	$	(23,581	)	$	1,617,388	$	(35,350	)

	Less than 12 months					12 months or longer					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
December 31, 2016	(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		)
Residential mortgage-backed securities	1,112,947		(16,900		)	—		—			1,112,947		(16,900		)
Commercial mortgage-backed securities	24,563		(537		)	—		—			24,563		(537		)
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	)

Summary of Amortized Cost and Fair Values of Corporate Debt Securities

The following table presents the amortized cost and estimated fair value of corporate debt securities:

	September 30, 2017				December 31, 2016
	Amortized cost		Estimated fair value		Amortized cost		Estimated fair value
	(in thousands)
Single-issuer trust preferred securities	$	39,186	$	38,251	$	43,746	$	39,829
Subordinated debt	37,147		37,859		46,231		46,723
Senior debt	12,033		12,456		18,037		18,433
Pooled trust preferred securities	—		422		—		422
Corporate debt securities issued by financial institutions	88,366		88,988		108,014		105,407
Other corporate debt securities	3,989		3,989		4,002		4,002
Available for sale corporate debt securities	$	92,355	$	92,977	$	112,016	$	109,409