Washington Banking Company Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 16, 2009
Assets [Abstract]
Cash and cash equivalents	$ 107,573				$ 105,913				$ 107,573	$ 105,913	$ 81,687
Other assets	20,042				20,080				20,042	20,080
Total assets	1,687,677				1,670,682				1,687,677	1,670,682
Liabilities [Abstract]
Junior subordinated debentures	25,774				25,774				25,774	25,774
Other liabilities	16,306				7,744				16,306	7,744
Total liabilities	1,505,053				1,499,862				1,505,053	1,499,862
Shareholders' Equity [Abstract]
Preferred stock											25,334		26,400
Common stock	85,707				84,564				85,707	84,564
Retained earnings	92,234				83,107				92,234	83,107
Accumulated other comprehensive income, net	4,683				3,149				4,683	3,149
Total shareholders' equity	182,624				170,820				182,624	170,820	182,098	159,521
Total liabilities and shareholders' equity	1,687,677				1,670,682				1,687,677	1,670,682
Interest income [Abstract]
Interest on taxable investment securities									5,333	3,967	2,348
Total interest income	21,439	22,262	22,726	23,283	23,040	22,512	22,157	21,998	89,710	89,707	75,949
Interest expense [Abstract]
Junior subordinated debentures									532	489	496
Total interest expense	1,585	1,710	1,837	1,981	2,171	2,430	2,669	2,711	7,113	9,981	11,830
Noninterest expense	13,972	13,663	15,109	13,655	14,291	13,807	13,671	14,056	56,399	55,825	46,797
Loss before income tax benefit and undistributed earnings of subsidiaries	6,739	6,997	4,020	6,944	6,137	5,206	5,757	5,963	24,700	23,063	37,367
Income tax benefit	(2,153)	(2,359)	(1,173)	(2,171)	(1,898)	(1,581)	(1,745)	(1,887)	(7,856)	(7,111)	(11,797)
Net income before preferred dividends					4,239	3,625	4,012	4,076	16,844	15,952	25,570
Preferred dividends										(38)	(1,320)
Net income available to common shareholders	4,586	4,638	2,847	4,773	4,239	3,625	4,012	2,992	16,844	14,868	23,911
Operating activities [Abstract]
Net income					4,239	3,625	4,012	4,076	16,844	15,952	25,570
Adjustments to reconcile net income to net cash used in operating activities [Abstract]
Net (increase) decrease in other assets									18,745	18,349	13,087
Net decrease in other liabilities									8,562	2,897	(19,334)
Net cash provided by operating activities									70,906	51,777	8,184
Investing activities [Abstract]
Net cash (used in) provided by investing activities									(58,490)	29,134	297,489
Financing activities [Abstract]
Redemption of preferred stock									0	(26,380)	0
Repurchase of common stock warrant									0	(1,625)	0
Dividends paid on preferred stock									0	(38)	(1,320)
Dividends paid on common stock									(7,717)	(3,068)	(2,067)
Proceeds from issuance of common stock under stock plans									301	301	104
Net cash used in financing activities									(10,756)	(56,685)	(325,827)
Net change in cash and cash equivalents									1,660	24,226	(20,154)
Cash and cash equivalents at beginning of period				105,913				81,687	105,913	81,687	101,841
Cash and cash equivalents at end of period	107,573				105,913				107,573	105,913	81,687
Washington Banking [Member]
Assets [Abstract]
Cash and cash equivalents	5,327				5,393				5,327	5,393	1,476
Investment in subsidiaries	201,345				190,033				201,345	190,033
Other assets	1,747				1,192				1,747	1,192
Total assets	208,419				196,618				208,419	196,618
Liabilities [Abstract]
Junior subordinated debentures	25,774				25,774				25,774	25,774
Other liabilities	21				24				21	24
Total liabilities	25,795				25,798				25,795	25,798
Shareholders' Equity [Abstract]
Preferred stock	0				0				0	0
Common stock	85,707				84,564				85,707	84,564
Retained earnings	92,234				83,107				92,234	83,107
Accumulated other comprehensive income, net	4,683				3,149				4,683	3,149
Total shareholders' equity	182,624				170,820				182,624	170,820
Total liabilities and shareholders' equity	208,419				196,618				208,419	196,618
Interest income [Abstract]
Interest on taxable investment securities									16	15	15
Total interest income									16	15	15
Interest expense [Abstract]
Junior subordinated debentures									532	489	496
Total interest expense									532	489	496
Noninterest expense									1,057	905	832
Loss before income tax benefit and undistributed earnings of subsidiaries									(1,573)	(1,379)	(1,313)
Income tax benefit									550	482	459
Loss before undistributed earnings of subsidiaries									(1,023)	(897)	(854)
Undistributed earnings of subsidiaries									8,967	11,949	25,924
Dividend income from Bank									8,900	4,900	500
Net income before preferred dividends									16,844	15,952	25,570
Preferred dividends									0	1,084	1,659
Net income available to common shareholders									16,844	14,868	23,911
Operating activities [Abstract]
Net income									16,844	15,952	25,570
Adjustments to reconcile net income to net cash used in operating activities [Abstract]
Equity in undistributed earnings of subsidiaries									(8,967)	(11,949)	(25,924)
Net (increase) decrease in other assets									(524)	(490)	128
Net decrease in other liabilities									(3)	(168)	(50)
Net cash provided by operating activities									7,350	3,345	(276)
Investing activities [Abstract]
Investment in subsidiaries									0	31,382	0
Net cash (used in) provided by investing activities									0	31,382	0
Financing activities [Abstract]
Redemption of preferred stock									0	(26,380)	0
Repurchase of common stock warrant									0	(1,625)	0
Dividends paid on preferred stock									0	(38)	(1,320)
Dividends paid on common stock									(7,717)	(3,068)	(2,067)
Proceeds from issuance of common stock under stock plans									301	301	104
Net cash used in financing activities									(7,416)	(30,810)	(3,283)
Net change in cash and cash equivalents									(66)	3,917	(3,559)
Cash and cash equivalents at beginning of period				5,393				1,476	5,393	1,476	5,035
Cash and cash equivalents at end of period	$ 5,327				$ 5,393				$ 5,327	$ 5,393	$ 1,476