Securities (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Fair Value of Available-for-sale and Held-to-maturity Securities

The amortized cost and fair value of securities available-for-sale and held-to-maturity at June 30, 2018 and December 31, 2017 are summarized as follows (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
June 30, 2018:
Securities available-for-sale:
U.S. Treasury securities	$	30,806	$	—	$	26	$	30,780
U.S. government agency securities	177,178		37		3,986		173,229
Mortgage-backed securities	1,269,307		3,866		34,142		1,239,031
State and municipal securities	1,220,415		3,775		17,009		1,207,181
Asset-backed securities	240,571		464		589		240,446
Corporate notes and other	69,827		724		1,090		69,461
	$	3,008,104	$	8,866	$	56,842	$	2,960,128
Securities held-to-maturity:
State and municipal securities	$	15,341	$	31	$	113	$	15,259
	$	15,341	$	31	$	113	$	15,259



December 31, 2017:
Securities available-for-sale:
U.S. Treasury securities	$	30,505	$	—	$	60	$	30,445
U.S. government agency securities	182,500		67		1,766		180,801
Mortgage-backed securities	1,270,625		5,318		12,124		1,263,819
State and municipal securities	774,949		12,251		2,588		784,612
Asset-backed securities	173,346		262		316		173,292
Corporate notes and other	81,615		1,346		647		82,314
	$	2,513,540	$	19,244	17,501		$	2,515,283
Securities held-to-maturity:
State and municipal securities	$	20,762	$	114	$	46	$	20,830
	$	20,762	$	114	$	46	$	20,830

Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

The amortized cost and fair value of debt securities as of June 30, 2018 by contractual maturity are shown below. Actual maturities may differ from contractual maturities of mortgage- and asset-backed securities since the mortgages and assets underlying the securities may be called or prepaid with or without penalty. Therefore, these securities are not included in the maturity categories in the following summary (in thousands):



	Available-for-sale				Held-to-maturity
June 30, 2018:	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due in one year or less	$	—	$	—	$	—	$	—
Due in one year to five years	102,756		102,863		6,412		6,405
Due in five years to ten years	176,890		175,583		8,015		7,941
Due after ten years	1,218,580		1,202,205		914		913
Mortgage-backed securities	1,269,307		1,239,031		—		—
Asset-backed securities	240,571		240,446		—		—
	$	3,008,104	$	2,960,128	$	15,341	$	15,259

Classification of Investments According to Term of Unrealized Losses of Less than Twelve Months or Twelve Months or Longer

At June 30, 2018 and December 31, 2017, the following investments had unrealized losses. The table below classifies these investments according to the term of the unrealized losses of less than twelve months or twelve months or longer (in thousands):



	Investments with an Unrealized Loss of less than 12 months				Investments with an Unrealized Loss of 12 months or longer				Total Investments with an Unrealized Loss
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
At June 30, 2018

U.S. Treasury securities	$	30,780	$	26	$	—	$	—	$	30,780	$	26
U.S. government agency securities	134,322		3,308		27,480		678		161,802		3,986
Mortgage-backed securities	720,677		19,811		339,377		14,331		1,060,054		34,142
State and municipal securities	860,821		14,143		62,029		2,979		922,850		17,122
Asset-backed securities	102,604		583		5,636		6		108,240		589
Corporate notes	33,468		963		4,471		127		37,939		1,090
Total temporarily-impaired securities	$	1,882,672	$	38,834	$	438,993	$	18,121	$	2,321,665	$	56,955

At December 31, 2017

U.S. Treasury securities	$	29,948	$	60	$	—	$	—	$	29,948	$	60
U.S. government agency securities	173,677		1,766		—		—		173,677		1,766
Mortgage-backed securities	607,408		5,042		285,561		7,082		892,969		12,124
State and municipal securities	115,403		1,408		50,083		1,226		165,486		2,634
Asset-backed securities	68,742		198		14,136		118		82,878		316
Corporate notes	22,168		547		11,944		100		34,112		647
Total temporarily-impaired securities	$	1,017,346	$	9,021	$	361,724	$	8,526	$	1,379,070	$	17,547