Basis and Summary of Significant Accounting Policies - Statements of Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,760,708	$ 1,728,004
Dividends	(2,363)	(2,146)
Stock-Based Compensation	7,050	7,862
Reissued Shares	(10,981)	(9,161)
Repurchased Shares		(18,407)
Net Earnings	56,078	52,246
Foreign Currency Translation Adjustment	424	(477)
Ending Balance	1,813,508	1,756,192
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ (567,847)	$ (407,713)
Beginning Balance (in shares)	(23,568)	(20,733)
Reissued Shares (in shares)	493	545
Reissued Shares	$ 4,264	$ 3,441
Repurchased Shares (in shares)		(391)
Repurchased Shares		$ (18,407)
Ending Balance (in shares)	(23,075)	(20,579)
Ending Balance	$ (563,583)	$ (422,679)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	45,376	45,376
Ending Balance	45,376	45,376
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	278,922	270,043
Stock-Based Compensation	7,050	7,862
Reissued Shares	(15,245)	(12,602)
Ending Balance	$ 270,727	$ 265,303
Retained Earnings
Dividends, per share (in dollars per share)	$ 0.035	$ 0.03
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 2,005,344	$ 1,819,524
Dividends	(2,363)	(2,146)
Net Earnings	56,078	52,246
Ending Balance	2,061,651	1,867,895
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(1,087)	774
Foreign Currency Translation Adjustment	424	(477)
Ending Balance	(663)	297
Accounting Standards Update 2014-09
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Opening Balance Sheet Adjustment - ASC 842, net of taxes		(1,729)
Accounting Standards Update 2014-09 \| Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Opening Balance Sheet Adjustment - ASC 842, net of taxes		$ (1,729)
Accounting Standards Update 2016-02
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Opening Balance Sheet Adjustment - ASC 842, net of taxes	2,592
Accounting Standards Update 2016-02 \| Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Opening Balance Sheet Adjustment - ASC 842, net of taxes	$ 2,592		$ 2,612

Aggregate dividends paid during the period for each share of common stock outstanding.

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