Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2016	Aug. 31, 2016
Stockholders' equity
Compensation cost not yet recognized			$ 14,000	$ 14,000
2015 Stock Incentive Plan | Nonvested stock units issued (NSUs)
Stockholders' equity
Vesting rights percent				33.33%
Number of shares granted			64,000	84,000
Award vesting period of the grants				3 years
Weighted average grant date fair value (in USD per share)			$ 68.55	$ 65.86
2015 Stock Incentive Plan | Time-based equity award
Stockholders' equity
Number of shares granted			105,000	156,000
Award vesting period of the grants				3 years
Weighted average grant date fair value (in USD per share)			$ 65.83	$ 62.83
2015 Employee Stock Purchase Plan
Stockholders' equity
Common stock reserved for issuance (in shares)		1,000,000
Employee stock purchase plan, purchase period	6 months
Employee stock purchase plan discount		15.00%
Stock Issued During Period, Shares, Employee Stock Purchase Plans					7,000,000
Shares Issued, Price Per Share					$ 55,550
2015 Stock Repurchase Program
Stockholders' equity
Treasury stock, number of shares held			1,797,000,000	1,797,000,000
Treasury stock acquired, average cost per share (in USD per share)				$ 67.95
Treasury stock, value			$ 122,100	$ 122,100
Remaining stock repurchase amount approved by Board of Directors			$ 77,900	$ 77,900