Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at Dec. 31, 2017	$ 884,778	$ 473	$ 260,157	$ 676,644	$ (12,496)	$ (40,000)
Balance (in shares) at Dec. 31, 2017		46,745
Increase (Decrease) in Stockholders' Equity
Net income	69,515			69,515
Translation adjustment, net of tax	7,583				7,583
Options exercised	695	$ 0	695
Options exercised (in shares)		23
Stock-based compensation	5,531		5,531
Shares issued from release of Restricted Stock Units	(5,111)	$ 2	(5,113)
Shares issued from release of Restricted Stock Units (in shares)		176
Repurchase of common stock	(25,439)		10,000			(35,439)
Repurchase of common stock (in shares)		(627)
Retirement of common stock	0	$ (13)		(74,986)		74,999
Cash dividends declared on common stock	(19,840)			(19,840)
Common stock issued	465		465
Common stock issued (in shares)		8
Balance at Jun. 30, 2018	903,802	$ 462	271,735	652,124	(20,079)	(440)
Balance (in shares) at Jun. 30, 2018		46,325
Balance at Dec. 31, 2017	884,778	$ 473	260,157	676,644	(12,496)	(40,000)
Balance (in shares) at Dec. 31, 2017		46,745
Increase (Decrease) in Stockholders' Equity
Net income	57,118			57,118
Translation adjustment, net of tax	5,328				5,328
Pension adjustment, net of tax	376				376
Stock-based compensation	4,803		4,803
Adoption of new accounting standards				(381)	381
Shares issued from release of Restricted Stock Units	(34)	$ 0	(34)
Shares issued from release of Restricted Stock Units (in shares)		1
Repurchase of common stock	(85,101)		0			(85,101)
Repurchase of common stock (in shares)		(1,328)
Retirement of common stock	0	$ (9)		(60,532)		60,541
Cash dividends declared on common stock	(20,122)			(20,122)
Balance at Dec. 31, 2018	855,514	$ 453	276,504	628,207	(24,650)	(25,000)
Balance (in shares) at Dec. 31, 2018		44,998
Increase (Decrease) in Stockholders' Equity
Net income	62,239			62,239
Translation adjustment, net of tax	(28)				28
Pension adjustment, net of tax	100				100
Stock-based compensation	6,127		6,127
Shares issued from release of Restricted Stock Units	(5,897)	$ 2	(5,899)
Shares issued from release of Restricted Stock Units (in shares)		177
Repurchase of common stock	(30,000)		0			(30,000)
Repurchase of common stock (in shares)		(505)
Retirement of common stock	0	$ (9)		(54,991)		55,000
Cash dividends declared on common stock	(19,926)			(19,926)
Common stock issued	292		292
Common stock issued (in shares)		5
Balance at Jun. 30, 2019	$ 868,421	$ 446	$ 277,024	$ 615,529	$ (24,578)	$ 0
Balance (in shares) at Jun. 30, 2019		44,675