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
Net income attributable to common shares	$ 15,643	$ 12,035	$ 31,935	$ 23,296
Weighted-average common shares outstanding - basic	33,835,727	32,022,845	33,698,022	31,137,769
Effect of potentially dilutive common shares:
Stock options	76,968	193,061	117,550	198,350
Unvested awards	141,121	219,700	194,358	218,038
Weighted-average common shares outstanding - diluted	34,053,816	32,435,606	34,009,930	31,554,157
Net income per share attributable to common shares
Basic (in dollars per share)	$ 0.46	$ 0.38	$ 0.95	$ 0.75
Diluted (in dollars per share)	$ 0.46	$ 0.37	$ 0.94	$ 0.74
Weighted-average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	562	0	92,260	118,940