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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 23,917	$ 23,587	$ 76,950	$ 53,373
Less: Net income allocated to unvested participating restricted stock	(795)	(799)	(2,621)	(1,793)
Net income available to common stockholders - basic	23,122	22,788	74,329	51,580
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	6	7	28	8
Net income available to common stockholders - diluted	$ 23,128	$ 22,795	$ 74,357	$ 51,588
Weighted average outstanding shares of common stock - basic (in shares)	16,762	17,439	17,095	17,562
Dilutive effect of stock options (in shares)	293	299	337	235
Weighted average outstanding shares of common stock - diluted (in shares)	17,055	17,738	17,432	17,797
Net income per common share - basic (USD per share)	$ 1.38	$ 1.31	$ 4.35	$ 2.94
Net income per common share - diluted (USD per share)	$ 1.36	$ 1.29	$ 4.27	$ 2.90