Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 17,644	$ 29,459	$ 48,938	$ 31,981
Denominator:
Weighted average shares outstanding (shares)	77,784	81,087	78,636	81,032
Diluted effect of stock awards (shares)	696	858	692	1,071
Weighted average shares outstanding assuming dilution (shares)	78,480	81,945	79,328	82,103
Basic earnings per share (in dollars per share)	$ 0.23	$ 0.36	$ 0.62	$ 0.39
Diluted earnings per share (in dollars per share)	$ 0.22	$ 0.36	$ 0.62	$ 0.39