Capital Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2016	Mar. 31, 2014	May 10, 2012
Class of Stock [Line Items]
Common Stock, Shares, Outstanding	95,727,000	107,012,000	111,469,000		117,173,000
Stock Issued During Period, Shares, Share-based Compensation, Gross	321,000	338,000	718,000
Stock Issued During Period, Shares, Employee Benefit Plan	16,000	12,000	44,000
Common Stock, Dividends, Per Share, Declared	$ 0.88	$ 0.80	$ 0.64
Dividends Payable	$ 21,153	$ 22,038	$ 17,837
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures	445,000	142,000	938,000
Common Stock, Shares Authorized	500,000,000	500,000,000
Preferred Stock, Shares Authorized	4,000,000
Common Stock, Capital Shares Reserved for Future Issuance	4,111,000	6,988,000
Stock Repurchase Program, Authorized Amount	$ 1,000,000					$ 1,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 423,000		$ 13,515
Stock Repurchased and Retired During Period, Shares	(11,697,000)	(4,537,000)	(6,931,000)
Shares Paid for Tax Withholding for Share Based Compensation	(370,000)	(412,000)	(473,000)
Stock Repurchased and Retired During Period, Value	$ 381,672	$ 209,632	$ 356,522
2.5% Convertible Senior Notes [Member]
Class of Stock [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	14,205,000			14,205,000