Net Income per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 31,643	$ 17,073
Less: Net income allocated to unvested participating restricted stock	(1,111)	(568)
Net income available to common stockholders - basic	30,532	16,505
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	12	2
Net income available to common stockholders - diluted	$ 30,544	$ 16,507
Weighted average outstanding shares of common stock - basic (in shares)	17,343	17,703
Dilutive effect of stock options (in shares)	347	142
Weighted average outstanding shares of common stock - diluted (in shares)	17,690	17,845
Net income per common share - basic (USD per share)	$ 1.76	$ 0.93
Net income per common share - diluted (USD per share)	$ 1.73	$ 0.92