Business Combinations (Pro Forma Results of Operations) (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Business Acquisition, Pro Forma Information [Abstract]
Net interest income	$ 219,730,000	$ 225,716,000	$ 653,786,000	$ 545,813,000
Provision for loan and lease losses	8,153,000	14,333,000	32,044,000	35,000,000
Non-interest income	60,349,000	62,165,000	204,343,000	130,869,000
Non-interest expense	182,686,000	182,558,000	577,681,000	493,207,000
Income before provision for income taxes	89,240,000	90,990,000	248,404,000	148,475,000
Provision for income taxes	31,633,000	32,107,000	88,884,000	53,399,000
Net income	57,607,000	58,883,000	159,520,000	95,076,000	$ 147,658,000
Dividends and undistributed earnings allocated to participating securities	84,000	142,000	261,000	338,000
Net earnings available to common shareholders	$ 57,523,000	$ 58,741,000	$ 159,259,000	$ 94,738,000
Earnings per share:
Basic (in usd per share)	$ 0.26	$ 0.27	$ 0.72	$ 0.54
Diluted (in usd per share)	$ 0.26	$ 0.27	$ 0.72	$ 0.54
Average shares outstanding:
Basic (in shares)	220,297	217,245	220,370	175,627
Diluted (in shares)	220,904	218,941	221,062	176,656
Footnote Information [Abstract]
Amortization of investment premiums, net			$ (18,135,000)	$ (15,320,000)
Change in junior subordinated debentures carried at fair value			$ (4,371,000)	(4,082,000)
Sterling Financial Corporation [Member] | Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net earnings available to common shareholders		$ 1,600,000		50,500,000
Pro Forma [Member] | Sterling Financial Corporation [Member]
Business Acquisition, Pro Forma Information [Abstract]
Net interest income		225,715,000		682,679,000
Provision for loan and lease losses		14,333,000		35,000,000
Non-interest income		62,163,000		157,134,000
Non-interest expense		179,918,000		565,573,000
Income before provision for income taxes		93,627,000		239,240,000
Provision for income taxes		33,122,000		88,325,000
Net income		60,505,000		150,915,000
Dividends and undistributed earnings allocated to participating securities		142,000		338,000
Net earnings available to common shareholders		$ 60,363,000		$ 150,577,000
Earnings per share:
Basic (in usd per share)		$ 0.28		$ 0.69
Diluted (in usd per share)		$ 0.28		$ 0.69
Average shares outstanding:
Basic (in shares)		217,245		216,884
Diluted (in shares)		218,941		218,801
Footnote Information [Abstract]
Accretion of loan discounts		$ 0		$ 31,900,000
Amortization of investment premiums, net		0		(1,800,000)
Amortization of deposit and borrowings premiums		0		(5,900,000)
Loss on service charges due to exceeding $10 billion asset threshold		0		(1,700,000)
Change in junior subordinated debentures carried at fair value		0		(1,100,000)
Reversal of provision for loss on divestiture				7,000,000
Amortization of core deposit intangibles		0		2,100,000
Adjustment to merger related expenses		$ (2,600,000)		$ (46,100,000)