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Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019	Apr. 30, 1997
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares repurchased under repurchase program		41,800,000	200,000
Cost of common shares repurchased	$ 22,845	$ 1,600,000	$ 22,800
Total number of shares repurchased pursuant to the repurchase program		41,836,234		41,836,234
Total cost of shares repurchased pursuant to the repurchase program		$ 1,623,256		$ 1,623,256
Additional shares that can be repurchased under the approved share repurchase program		12,900,000
Preferred stock, shares authorized		2,000,000		2,000,000
Preferred stock at par value		$ 0.01		$ 0.01
Preferred stock, shares issued		0		0
Shares issued under Employee Stock Purchase Plan		137,000	129,000
Treasury Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares repurchased under repurchase program	200,000
Cost of common shares repurchased	$ 22,844
Series A Junior Participating Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized					2,000,000.0
Preferred stock at par value					$ 0.01
Preferred stock, shares issued		0		0
Preferred stock, shares outstanding		0		0
2009 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		7 years
Common stock authorized for issuance		51,100,000
Number of securities remaining available for future issuance		15,000,000.0
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities remaining available for future issuance		2,100,000
Minimum [Member] \| 2009 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Maximum [Member] \| 2009 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years