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
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Business Acquisition, Pro Forma Information [Abstract]
Net interest income	$ 215,908,000	$ 107,838,000
Provision for loan and lease losses	12,637,000	5,971,000
Non-interest income	63,595,000	23,238,000
Non-interest expense	193,098,000	96,518,000
Income before income taxes	73,768,000	28,587,000
Provision for income taxes	26,639,000	9,936,000
Net income	47,129,000	18,651,000	147,658,000
Dividends and undistributed earnings allocated to participating securities	84,000	113,000
Net earnings available to common shareholders	47,045,000	18,538,000
Earnings per share:
Basic (in usd per share)	$ 0.21	$ 0.17
Diluted (in usd per share)	$ 0.21	$ 0.16
Average shares outstanding:
Basic (in shares)	220,349	112,170
Diluted (in shares)	221,051	112,367
Footnote Information [Abstract]
Amortization of investment premiums, net	(5,605,000)	(4,000,000)
Change in junior subordinated debentures carried at fair value	(1,358,000)	(526,000)
Sterling Financial Corporation [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders		16,100,000
Pro Forma [Member] | Sterling Financial Corporation [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income		222,766,000
Provision for loan and lease losses		5,971,000
Non-interest income		45,018,000
Non-interest expense		188,488,000
Income before income taxes		73,325,000
Provision for income taxes		26,073,000
Net income		47,252,000
Dividends and undistributed earnings allocated to participating securities		113,000
Net earnings available to common shareholders		47,139,000
Earnings per share:
Basic (in usd per share)		$ 0.22
Diluted (in usd per share)		$ 0.22
Average shares outstanding:
Basic (in shares)		216,438
Diluted (in shares)		217,523
Footnote Information [Abstract]
Accretion of loan discounts		26,700,000
Amortization of investment premiums, net			(1,500,000)
Amortization of deposit and borrowings premiums		4,900,000
Loss on service charges due to exceeding $10 billion asset threshold		1,400,000
Change in junior subordinated debentures carried at fair value		(952,000)
Reversal of provision for loss on divestiture		7,000,000
Adjustment to merger related expenses			5,400,000
Amortization of core deposit intangibles		$ 1,700,000