Acquisitions (Pro forma) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Net income	$ 21,632	$ 20,208	$ 61,600	$ 61,187
Citywide Banks
Business Acquisition [Line Items]
Net interest income			264,485	256,579
Net income available to common stockholders			$ 61,940	$ 68,857
Basic earnings per share (in dollars per share)			$ 2.08	$ 2.51
Diluted earnings per share (in dollars per share)			$ 2.06	$ 2.48
Transaction costs			$ 3,800
Citywide Banks | Acquisition-related Costs
Business Acquisition [Line Items]
Net income			$ (10,100)