Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Combinations [Abstract]
Total revenue (net interest income plus other income)	$ 380,324	$ 353,732
Net income	95,009	95,288
Net income available to common shareholders
Earnings per share:
Basic (in dollars per share)	$ 1.94	$ 1.95
Diluted (in dollars per share)	$ 1.93	$ 1.94