Securities (Tables)

12 Months Ended

Dec. 31, 2015

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, 2015	(in thousands)
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	1,296,955	$	4,525	$	(14,991	)	$	1,286,489
State and municipal securities	480,417		12,690		(938		)	492,169
U.S. government agency and government-sponsored enterprise securities	354,515		1,113		(1,846		)	353,782
U.S. government securities	20,439		—		(302		)	20,137
Other securities	5,284		24		(191		)	5,117
Total	$	2,157,610	$	18,352	$	(18,268	)	$	2,157,694
December 31, 2014
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	1,160,378	$	10,219	$	(8,210	)	$	1,162,387
State and municipal securities	483,578		14,432		(1,526		)	496,484
U.S. government agency and government-sponsored enterprise securities	416,919		856		(4,069		)	413,706
U.S. government securities	20,910		—		(411		)	20,499
Other securities	5,284		20		(123		)	5,181
Total	$	2,087,069	$	25,527	$	(14,339	)	$	2,098,257

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

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

	Years Ended December 31,
	2015			2014			2013
	(in thousands)
Gross realized gains	$	1,591		$	553		$	632
Gross realized losses	(10		)	(1		)	(170		)
Net realized gains	$	1,581		$	552		$	462

Schedule of Contractual Maturities of Investment Securities Available for Sale

The scheduled contractual maturities of investment securities available for sale at December 31, 2015 are presented as follows:

	December 31, 2015
	Amortized Cost		Fair Value
	(in thousands)
Due within one year	$	22,191	$	22,418
Due after one year through five years	458,889		458,372
Due after five years through ten years	702,234		703,088
Due after ten years	969,012		968,699
Other securities with no stated maturity	5,284		5,117
Total investment securities available-for-sale	$	2,157,610	$	2,157,694

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, 2015		December 31, 2014
	(in thousands)
Washington and Oregon State to secure public deposits	$	341,079	$	328,400
Federal Reserve Bank to secure borrowings	48,714		41,146
Other securities pledged	143,606		157,097
Total securities pledged as collateral	$	533,399	$	526,643

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, 2015 and 2014:

	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2015	(in thousands)
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	664,509	$	(7,610	)	$	214,325	$	(7,381	)	$	878,834	(14,991		)
State and municipal securities	48,261		(358		)	31,383		(580		)	79,644		(938		)
U.S. government agency and government-sponsored enterprise securities	193,400		(1,128		)	40,034		(718		)	233,434		(1,846		)
U.S. government securities	10,343		(136		)	9,794		(166		)	20,137		(302		)
Other securities	2,300		(15		)	2,780		(176		)	5,080		(191		)
Total	$	918,813	$	(9,247	)	$	298,316	$	(9,021	)	$	1,217,129	$	(18,268	)
December 31, 2014
U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations	$	258,825	$	(1,287	)	$	279,015	$	(6,924	)	$	537,840	$	(8,211	)
State and municipal securities	71,026		(543		)	44,148		(982		)	115,174		(1,525		)
U.S. government agency and government-sponsored enterprise securities	105,250		(518		)	216,221		(3,551		)	321,471		(4,069		)
U.S. government securities	—		—			19,450		(411		)	19,450		(411		)
Other securities	2,313		(2		)	2,834		(121		)	5,147		(123		)
Total	$	437,414	$	(2,350	)	$	561,668	$	(11,989	)	$	999,082	$	(14,339	)