Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 52,014	$ 25,775	$ 99,618	$ 49,380
Net income allocated to participating securities	219	0	446	0
Net income allocated to common shareholders	$ 51,795	$ 25,775	$ 99,172	$ 49,380
Weighted average common shares - issued (in shares)	71,122,000	38,258,000	71,046,000	38,228,000
Average unvested restricted share awards (in shares)	(303,000)	0	(321,000)	0
Weighted average common shares outstanding - basic (in shares)	70,819,000	38,258,000	70,725,000	38,228,000
Effect of dilutive securities
Weighted average common stock equivalents (in shares)	624,000	342,000	704,000	332,000
Weighted average common shares outstanding - diluted (in shares)	71,443,000	38,600,000	71,429,000	38,560,000
EPS available to common shareholders
Basic earnings per common share (dollars per share)	$ 0.73	$ 0.67	$ 1.41	$ 1.29
Diluted earnings per common share (dollars per share)	0.73	0.67	1.39	1.28
Average stock valuation (dollars per share)	$ 47.78	$ 37.80	$ 49.78	$ 35.55
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)	125,782	0	90,537	0