Securities (Tables)

9 Months Ended

Sep. 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 September 30, 2018 and December 31, 2017 are summarized as follows (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
September 30, 2018:
Securities available-for-sale:
U.S. Treasury securities	$	30,573	$	—	$	45	$	30,528
U.S. government agency securities	64,640		45		1,500		63,185
Mortgage-backed securities	1,334,640		3,268		43,363		1,294,545
State and municipal securities	1,240,136		1,995		29,860		1,212,271
Asset-backed securities	334,547		870		759		334,658
Corporate notes and other	69,738		617		960		69,395
	$	3,074,274	$	6,795	$	76,487	$	3,004,582
Securities held-to-maturity:
State and municipal securities	$	194,997	$	9	$	2,506	$	192,500
	$	194,997	$	9	$	2,506	$	192,500

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 September 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
September 30, 2018:	Amortized Cost		Fair Value		Amortized  Cost		Fair Value
Due in one year or less	$	34,856	$	34,802	$	315	$	316
Due in one year to five years	77,055		77,059		6,066		6,044
Due in five years to ten years	159,471		157,274		7,997		7,875
Due after ten years	1,133,705		1,106,244		180,619		178,265
Mortgage-backed securities	1,334,640		1,294,545		—		—
Asset-backed securities	334,547		334,658		—		—
	$	3,074,274	$	3,004,582	$	194,997	$	192,500

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

At September 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 September 30, 2018
U.S. Treasury securities	$	30,284	$	39	$	244	$	6	$	30,528	$	45
U.S. government agency securities	13,605		360		45,118		1,140		58,723		1,500
Mortgage-backed securities	289,149		5,951		807,418		37,412		1,096,567		43,363
State and municipal securities	1,144,600		29,599		108,653		5,663		1,253,253		35,262
Asset-backed securities	204,638		741		4,505		18		209,143		759
Corporate notes	22,329		260		18,681		700		41,010		960
Total temporarily-impaired securities	$	1,704,605	$	36,950	$	984,619	$	44,939	$	2,689,224	$	81,889
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