Earnings Per Share (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
Earnings Per Share
Net income attributable to common shares	$ 15,758	$ 12,180	$ 47,693	$ 35,476
Weighted-average common shares outstanding - basic	33,878,881	33,425,762	33,758,971	31,906,000
Effect of potentially dilutive common shares:
Stock options	59,201	192,272	98,660	197,166
Unvested awards	176,087	294,121	176,211	258,201
Weighted-average common shares outstanding - diluted	34,114,169	33,912,155	34,033,842	32,361,367
Net income per share attributable to common shares
Basic (in dollars per share)	$ 0.47	$ 0.36	$ 1.41	$ 1.11
Diluted (in dollars per share)	$ 0.46	$ 0.36	$ 1.40	$ 1.10
Weighted-average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	1,205	7,757	109,953	113,920