Basis and Summary of Significant Accounting Policies - Statements of Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,446,614	$ 1,737,259	$ 1,813,508	$ 1,760,708	$ 1,737,259	$ 1,760,708	$ 1,760,708
Cash Dividends	(2,701)	(2,700)	(2,386)	(2,363)
Stock-Based Compensation	6,856	5,878	6,522	7,050
Reissued Shares	1,722	(5,349)	3,060	(10,981)
Repurchased Shares			(14,414)
Net (Loss) Earnings	68,377	(280,005)	42,650	56,078	(211,628)	98,728
Foreign Currency Translation Adjustment	331	(1,754)	618	424	(1,423)	1,042
Ending Balance	$ 1,521,199	1,446,614	$ 1,849,558	$ 1,813,508	1,521,199	1,849,558	$ 1,737,259
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201602Member			us-gaap:AccountingStandardsUpdate201613Member
Revision of prior period, accounting standards update, adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		$ (6,715)		$ 2,592	$ (6,715)	$ 2,592	$ 2,592
Ending Balance							$ (6,715)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)	(23,666)	(24,034)	(23,075)	(23,568)	(24,034)	(23,568)	(23,568)
Beginning Balance	$ (620,649)	$ (627,940)	$ (563,583)	$ (567,847)	$ (627,940)	$ (567,847)	$ (567,847)
Reissued Shares (in shares)	53	368	113	493
Reissued Shares	$ 1,392	$ 7,291	$ 2,776	$ 4,264
Repurchased Shares (in shares)			(243)
Repurchased Shares			$ (14,414)
Ending Balance (in shares)	(23,613)	(23,666)	(23,205)	(23,075)	(23,613)	(23,205)	(24,034)
Ending Balance	$ (619,257)	$ (620,649)	$ (575,221)	$ (563,583)	$ (619,257)	$ (575,221)	$ (627,940)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	45,376	45,376	45,376	45,376	45,376	45,376	45,376
Ending Balance	45,376	45,376	45,376	45,376	45,376	45,376	45,376
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	283,467	290,229	270,727	278,922	290,229	278,922	278,922
Stock-Based Compensation	6,856	5,878	6,522	7,050
Reissued Shares	330	(12,640)	284	(15,245)
Ending Balance	290,653	283,467	277,533	270,727	290,653	277,533	290,229
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	1,740,193	2,029,613	2,061,651	2,005,344	2,029,613	2,005,344	2,005,344
Cash Dividends	(2,701)	(2,700)	(2,386)	(2,363)
Net (Loss) Earnings	68,377	(280,005)	42,650	56,078
Ending Balance	$ 1,805,869	$ 1,740,193	$ 2,101,915	$ 2,061,651	1,805,869	2,101,915	2,029,613
Dividends, per share (in dollars per share)	$ 0.04	$ 0.04	$ 0.035	$ 0.035
Retained Earnings | Revision of prior period, accounting standards update, adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		$ (6,715)		$ 2,592	(6,715)	2,592	2,592
Ending Balance							(6,715)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ (1,773)	(19)	$ (663)	(1,087)	(19)	(1,087)	(1,087)
Foreign Currency Translation Adjustment	331	(1,754)	618	424
Ending Balance	$ (1,442)	$ (1,773)	$ (45)	$ (663)	$ (1,442)	$ (45)	$ (19)