Earnings Per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income to shareholders	$ 15,633	$ 18,450
Weighted average common shares outstanding:
Basic (in shares)	29,764,320	29,289,588
Common share equivalents (in shares)	428,983	1,037,835
Diluted (in shares)	30,193,303	30,327,423
Earnings per share:
Basic (in dollars per share)	$ 0.53	$ 0.63
Common share equivalents (in dollars per share)	(0.01)	(0.02)
Diluted (in dollars per share)	$ 0.52	$ 0.61