Business Combinations (Pro Forma Results of Operations) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition, Pro Forma Information [Abstract]
Net interest income	$ 219,834	$ 219,215	$ 217,466	$ 215,119	$ 228,015	$ 225,716	$ 212,259	$ 107,838		$ 871,634	$ 773,828	$ 404,965
Provision for loan and lease losses	4,545	8,153	11,254	12,637	5,241	14,333	14,696	5,971		36,589	40,241	10,716
Non-interest income	69,345	61,372	81,102	63,905	50,305	62,165	45,466	23,238		275,724	181,174	122,895
Non-interest expense	185,911	183,194	201,918	192,619	190,856	182,558	214,131	96,518		763,642	684,063	364,661
Income before income taxes	98,723	89,240	85,396	73,768	82,223	90,990	28,898	28,587		347,127	230,698	152,483
Provision for income taxes	35,704	31,633	30,612	26,639	29,641	32,107	11,356	9,936		124,588	83,040	54,192
Net income	63,019	57,607	54,784	47,129	52,582	58,883	17,542	18,651		222,539	147,658	98,291
Dividends and undistributed earnings allocated to participating securities	96	84	93	84	146	142	83	113		357	484	788
Net earnings available to common shareholders	$ 62,923	$ 57,523	$ 54,691	$ 47,045	$ 52,436	$ 58,741	$ 17,459	$ 18,538		$ 222,182	$ 147,174	$ 97,503
Earnings per share:
Basic earnings per common share (usd per share)	$ 0.29	$ 0.26	$ 0.25	$ 0.21	$ 0.24	$ 0.27	$ 0.09	$ 0.17		$ 1.01	$ 0.79	$ 0.87
Diluted earnings per common share (usd per share)	$ 0.28	$ 0.26	$ 0.25	$ 0.21	$ 0.24	$ 0.27	$ 0.09	$ 0.16		$ 1.01	$ 0.78	$ 0.87
Average shares outstanding:
Basic (in shares)										220,327	186,550	111,938
Diluted (in shares)										221,045	187,544	112,176
Footnote Information [Abstract]
Amortization of investment premiums, net										$ (23,544)	$ (20,822)	$ (32,663)
Change in junior subordinated debentures carried at fair value										$ (6,163)	(5,849)	(2,193)
Sterling Financial Corporation [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders											54,400	12,900
Financial Pacific Holding Corp [Member]
Business Acquisition, Pro Forma Information [Abstract]
Non-interest expense									$ 15,900
Net income									$ 18,700
Financial Pacific Holding Corp [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders												4,200
Pro Forma [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income												423,600
Provision for loan and lease losses												13,988
Non-interest income												122,753
Non-interest expense												373,181
Income before income taxes												159,184
Provision for income taxes												55,879
Net income												103,305
Dividends and undistributed earnings allocated to participating securities												829
Net earnings available to common shareholders												$ 102,476
Earnings per share:
Basic earnings per common share (usd per share)												$ 0.92
Diluted earnings per common share (usd per share)												$ 0.91
Average shares outstanding:
Basic (in shares)												111,938
Diluted (in shares)												112,176
Pro Forma [Member] | Sterling Financial Corporation [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income											910,715	$ 873,972
Provision for loan and lease losses											40,241	10,716
Non-interest income											205,557	242,609
Non-interest expense											750,069	802,371
Income before income taxes											325,962	303,494
Provision for income taxes											118,679	98,603
Net income											207,283	204,891
Dividends and undistributed earnings allocated to participating securities											484	788
Net earnings available to common shareholders											$ 206,799	$ 204,103
Earnings per share:
Basic earnings per common share (usd per share)											$ 0.91	$ 0.94
Diluted earnings per common share (usd per share)											$ 0.90	$ 0.93
Average shares outstanding:
Basic (in shares)											227,807	216,025
Diluted (in shares)											229,690	218,508
Footnote Information [Abstract]
Accretion of loan discounts											$ 31,900	$ 127,500
Amortization of investment premiums, net											(1,800)	(6,600)
Amortization of deposit and borrowings premiums											(5,900)	(22,100)
Loss on service charges due to exceeding $10 billion asset threshold											1,700	5,800
Change in junior subordinated debentures carried at fair value											(1,100)	(3,900)
Reversal of provision for loss on divestiture											7,000
Amortization of core deposit intangibles											2,100	7,800
Increase (decrease) in merger related expenses											$ (52,600)	$ 98,200