Securities (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Available-for-sale Securities [Line Items]

Securities Available for Sale

The following table summarizes the amortized cost, gross unrealized gains and losses and the resulting fair value of securities available for sale:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
December 31, 2017	(in thousands)
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	1,752,236	$	1,815	$	(27,326	)	$	1,726,725
State and municipal securities	593,940		6,023		(3,959		)	596,004
U.S. government agency and government-sponsored enterprise securities	416,894		642		(2,762		)	414,774
U.S. government securities	251		—		(3		)	248
Other securities	5,284		84		(288		)	5,080
Total	$	2,768,605	$	8,564	$	(34,338	)	$	2,742,831
December 31, 2016
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	1,486,690	$	2,760	$	(23,718	)	$	1,465,732
State and municipal securities	473,914		6,343		(5,197		)	475,060
U.S. government agency and government-sponsored enterprise securities	332,348		1,065		(1,511		)	331,902
U.S. government securities	801		—		(1		)	800
Other securities	5,284		63		(264		)	5,083
Total	$	2,299,037	$	10,231	$	(30,691	)	$	2,278,577

Schedule of gross realized gains and losses on sales and calls of securities available for sale [Table Text Block]

The following table provides the proceeds and gross realized gains and losses on the sales and calls of securities for the periods indicated:

	Years Ended December 31,
	2017			2016		2015
	(in thousands)
Proceeds from sales and calls of available for sale securities	$	30,403		$	124,142	$	95,375
Gross realized gains	$	111		$	1,181	$	1,591
Gross realized losses	(122		)	—		(10		)
Net realized gains	$	(11	)	$	1,181	$	1,581

Schedule of Contractual Maturities of Investment Securities Available for Sale

The scheduled contractual maturities of investment securities available for sale at December 31, 2017 are presented as follows:

	December 31, 2017
	Amortized Cost		Fair Value
	(in thousands)
Due within one year	$	124,885	$	124,763
Due after one year through five years	638,921		636,860
Due after five years through ten years	804,462		796,611
Due after ten years	1,195,053		1,179,517
Other securities with no stated maturity	5,284		5,080
Total investment securities available-for-sale	$	2,768,605	$	2,742,831

Schedule of Securities pledged as collateral [Table Text Block]

The following table summarizes the carrying value of securities pledged as collateral to secure public deposits, borrowings and other purposes as permitted or required by law:

	December 31, 2017		December 31, 2016
	(in thousands)
Washington and Oregon State to secure public deposits	$	245,222	$	232,714
Federal Reserve Bank to secure borrowings	52,917		33,825
Other securities pledged	121,244		132,350
Total securities pledged as collateral	$	419,383	$	398,889

Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses

The following tables show the gross unrealized losses and fair value of the Company’s investments with unrealized losses that are not deemed to be other-than-temporarily impaired, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2017 and 2016:

	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2017	(in thousands)
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	816,678	$	(6,710	)	$	717,211	$	(20,616	)	$	1,533,889	(27,326		)
State and municipal securities	220,019		(1,723		)	75,172		(2,236		)	295,191		(3,959		)
U.S. government agency and government-sponsored enterprise securities	184,046		(1,006		)	155,983		(1,756		)	340,029		(2,762		)
U.S. government securities	249		(3		)	—		—			249		(3		)
Other securities	—		—			4,982		(288		)	4,982		(288		)
Total	$	1,220,992	$	(9,442	)	$	953,348	$	(24,896	)	$	2,174,340	$	(34,338	)
December 31, 2016
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	1,029,116	$	(18,788	)	$	159,046	$	(4,930	)	$	1,188,162	$	(23,718	)
State and municipal securities	211,342		(5,064		)	3,384		(133		)	214,726		(5,197		)
U.S. government agency and government-sponsored enterprise securities	218,811		(1,511		)	—		—			218,811		(1,511		)
U.S. government securities	251		(1		)	—		—			251		(1		)
Other securities	2,263		(51		)	2,743		(213		)	5,006		(264		)
Total	$	1,461,783	$	(25,415	)	$	165,173	$	(5,276	)	$	1,626,956	$	(30,691	)