CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Beginning Balance at Dec. 31, 2017	$ 941,597		$ 746,547	$ 194,971	$ 79
Beginning Balance (in shares) at Dec. 31, 2017		76,825,966
Issuance of restricted stock units	3,679		3,679
Issuance of restricted stock units (in shares)		645,047
Net income	20,855			20,855
Shares withheld related to net share settlement of stock awards	(7,502)		(7,502)
Shares withheld related to net share settlement of stock awards (in shares)		(229,898)
Ending Balance at Mar. 31, 2018	958,629		742,724	215,826	79
Ending Balance (in shares) at Mar. 31, 2018		77,241,115
Beginning Balance at Dec. 31, 2018	1,029,153	$ 1	748,076	290,206	1	$ (9,131)
Beginning Balance (in shares) at Dec. 31, 2018		77,438,889				223,823
Cumulative change in accounting principle, net of tax	(4,744)			(4,744)
Issuance of restricted stock units	4,948		4,948
Issuance of restricted stock units (in shares)		330,641
Net income	38,229			38,229
Shares withheld related to net share settlement of stock awards	(4,322)		(4,322)
Shares withheld related to net share settlement of stock awards (in shares)		(106,542)
Ending Balance at Mar. 31, 2019	$ 1,063,264	$ 1	$ 748,702	$ 323,691	$ 1	$ (9,131)
Ending Balance (in shares) at Mar. 31, 2019		77,662,988				223,823