Earnings Per Share - Basic and Diluted Earnings Per 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 to shareholders	$ 14,541	$ 14,596	$ 32,991	$ 27,433
Weighted average common shares outstanding:
Basic (in shares)	29,406,877	29,035,512	29,348,557	28,994,260
Common share equivalents (in shares)	900,222	790,402	969,028	789,823
Diluted (in shares)	30,307,099	29,825,914	30,317,585	29,784,083
Earnings per share:
Basic (in dollars per share)	$ 0.49	$ 0.50	$ 1.12	$ 0.95
Common share equivalents (in dollars per share)	(0.01)	(0.01)	(0.03)	(0.03)
Diluted (in dollars per share)	$ 0.48	$ 0.49	$ 1.09	$ 0.92