Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share
Net income attributable to common shares	$ 20,302	$ 16,292
Weighted-average common shares outstanding - basic	33,935,564	33,558,787
Effect of potentially dilutive common shares:
Stock options	53,813	156,035
Unvested awards	174,858	266,954
Weighted-average common shares outstanding - diluted	34,164,235	33,981,776
Net income per share attributable to common shares
Basic (in dollars per share)	$ 0.60	$ 0.49
Diluted (in dollars per share)	$ 0.59	$ 0.48
Weighted-average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	37,760	39,937