Debt (Details) - Senior Notes - USD ($)	Apr. 30, 2016	Mar. 31, 2016
Senior Notes due September 2016
Debt Instrument [Line Items]
Aggregate principal amount		$ 175,000,000
Stated interest rate		5.75%
Subsequent Event | Senior Notes due June 2026
Debt Instrument [Line Items]
Aggregate principal amount	$ 100,000,000
Stated interest rate	2.95%
Subsequent Event | Senior Notes due September 2046
Debt Instrument [Line Items]
Aggregate principal amount	$ 200,000,000
Stated interest rate	4.12%
Subsequent Event | Senior Notes due October 2046
Debt Instrument [Line Items]
Aggregate principal amount	$ 100,000,000
Stated interest rate	4.12%