Business Combinations (Pro Forma Results of Operations) (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Business Acquisition, Pro Forma Information [Abstract]
Net interest income	$ 228,015,000	$ 225,716,000	$ 212,259,000	$ 107,838,000	$ 110,074,000	$ 106,809,000	$ 93,893,000	$ 94,189,000	$ 773,828,000	$ 404,965,000	$ 407,236,000
Provision for loan and lease losses	5,241,000	14,333,000	14,696,000	5,971,000	2,471,000	1,104,000	(79,000)	7,220,000	40,241,000	10,716,000	29,201,000
Non-interest income	49,832,000	61,924,000	44,529,000	23,007,000	26,785,000	26,144,000	34,497,000	34,015,000	179,292,000	121,441,000	136,829,000
Non-interest expense	190,856,000	182,558,000	214,131,000	96,518,000	95,364,000	95,604,000	87,931,000	85,762,000	684,063,000	364,661,000	359,652,000
Income before income taxes	81,750,000	90,749,000	27,961,000	28,356,000	39,024,000	36,245,000	40,538,000	35,222,000	228,816,000	151,029,000	155,212,000
Provision for income taxes	29,204,000	31,760,000	10,740,000	9,592,000	13,754,000	12,768,000	14,285,000	11,861,000	81,296,000	52,668,000	53,321,000
Net income	52,546,000	58,989,000	17,221,000	18,764,000	25,270,000	23,477,000	26,253,000	23,361,000	147,520,000	98,361,000	101,891,000
Net earnings available to common shareholders	146,000	142,000	83,000	113,000	212,000	196,000	197,000	183,000	484,000	788,000	682,000
Net earnings available to common shareholders	52,400,000	58,847,000	17,138,000	18,651,000	25,058,000	23,281,000	26,056,000	23,178,000	147,036,000	97,573,000	101,209,000
Earnings per share:
Basic earnings per common share (usd per share)	$ 0.24	$ 0.27	$ 0.09	$ 0.17	$ 0.22	$ 0.21	$ 0.23	$ 0.21	$ 0.79	$ 0.87	$ 0.90
Diluted earnings per common share (usd per share)	$ 0.24	$ 0.27	$ 0.09	$ 0.17	$ 0.22	$ 0.21	$ 0.23	$ 0.21	$ 0.78	$ 0.87	$ 0.90
Average shares outstanding:
Basic (in shares)									186,550	111,938	111,935
Diluted (in shares)									187,544	112,176	112,151
Footnote Information [Abstract]
Amortization of investment premiums, net									(20,822,000)	(32,663,000)	(45,082,000)
Change in junior subordinated debentures carried at fair value									(5,849,000)	(2,193,000)	(2,175,000)
Sterling Financial Corporation [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income												339,254,000
Provision for loan losses												19,998,000
Non-interest income												82,212,000
Non-interest expense, excluding merger expense												227,007,000
Merger related expense												73,255,000
Income tax provision												(36,473,000)
Net income												64,733,000
Sterling Financial Corporation [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders									82,400,000	12,900,000
Financial Pacific Holding Corp [Member]
Business Acquisition, Pro Forma Information [Abstract]
Non-interest expense									15,900,000
Net income									18,700,000
Financial Pacific Holding Corp [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders										4,200,000
Pro Forma [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income									423,600,000
Provision for loan and lease losses									13,988,000
Non-interest income									122,753,000
Non-interest expense									373,181,000
Income before income taxes									159,184,000
Provision for income taxes									55,879,000
Net income									103,305,000
Net earnings available to common shareholders									829,000
Net earnings available to common shareholders									102,476,000
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									910,715,000	873,972,000
Provision for loan and lease losses									40,241,000	10,716,000
Non-interest income									205,557,000	242,609,000
Non-interest expense									704,488,000	802,371,000
Income before income taxes									371,543,000	303,494,000
Provision for income taxes									136,228,000	98,603,000
Net income									235,315,000	204,891,000
Net earnings available to common shareholders									484,000	788,000
Net earnings available to common shareholders									234,831,000	204,103,000
Earnings per share:
Basic earnings per common share (usd per share)									$ 1.03	$ 0.94
Diluted earnings per common share (usd per share)									$ 1.02	$ 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									31,900,000	127,500,000
Amortization of investment premiums, net									(1,800,000)	(6,600,000)
Amortization of deposit and borrowings premiums									(5,900,000)	(22,100,000)
Loss on service charges due to exceeding $10 billion asset threshold									1,700,000	5,800,000
Change in junior subordinated debentures carried at fair value									(1,100,000)	(3,900,000)
Reversal of provision for loss on divestiture									7,000,000
Amortization of core deposit intangibles									2,100,000	7,800,000
Adjustment to merger related expenses									$ 98,200,000