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Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Nov. 30, 2018	Jun. 30, 2018	Apr. 30, 1997
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares repurchased under repurchase program				200,000	300,000
Cost of common shares repurchased	$ 22,845	$ 19,357	$ 8,541	$ 22,800	$ 27,900
Total number of shares repurchased pursuant to the repurchase program				41,836,234			41,636,234
Total cost of shares repurchased pursuant to the repurchase program				$ 1,623,256			$ 1,600,412
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
Treasury Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares repurchased under repurchase program	200,000	200,000	100,000
Cost of common shares repurchased	$ 22,844	$ 19,356	$ 8,541
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
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				16,300,000
Amended And Restated 2009 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for issuance						6,200,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities remaining available for future issuance				2,400,000
Shares issued under Employee Stock Purchase Plan				129,000	148,000
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