Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 108,032	$ 86,830	$ 62,121
Net income allocated to participating securities									166	0	0
Net income allocated to common shareholders									$ 107,866	$ 86,830	$ 62,121
Weighted average common shares - issued (in shares)									49,091,000	36,081,000	31,367,000
Average unvested restricted share awards (in shares)									(139,000)	0	0
Weighted average common shares outstanding - basic (in shares)									48,952,000	36,081,000	31,367,000
Effect of dilutive securities
Weighted average common stock equivalents (in shares)									651,000	272,000	221,000
Weighted average common shares outstanding - diluted (in shares)									49,603,000	36,353,000	31,588,000
EPS available to common shareholders
Basic earnings per common share (usd per share)	$ 0.67	$ 0.23	$ 0.67	$ 0.61	$ 0.67	$ 0.64	$ 0.54	$ 0.54	$ 2.21	$ 2.41	$ 1.98
Diluted earnings per common share (usd per share)	$ 0.66	$ 0.23	$ 0.67	$ 0.60	$ 0.66	$ 0.64	$ 0.54	$ 0.54	2.17	2.39	1.97
Schedule Of Earnings Per Share By Common Class [Line Items]
Average stock valuation (usd per share)									$ 40.58	$ 32.17	$ 29.11
Stock Option
Schedule Of Earnings Per Share By Common Class [Line Items]
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share (in shares)									0	54,771	240,165