Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share
Net income attributable to common shares	$ 19,661	$ 20,302
Weighted-average common shares outstanding - basic	36,347,781	33,935,564
Effect of potentially dilutive common shares:
Stock options	38,921	53,813
Unvested awards	160,363	174,858
Weighted-average common shares outstanding - diluted	36,547,065	34,164,235
Net income per share attributable to common shares
Basic (in dollars per share)	$ 0.54	$ 0.60
Diluted (in dollars per share)	$ 0.54	$ 0.59
Weighted-average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	39,754	37,760