Derivative and Other Fair Value Instruments (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
2.375% Notes [Member]
Derivative [Line Items]
Proceeds from Issuance of Unsecured Debt	$ 450,000
Debt Instrument, Interest Rate, Stated Percentage	2.375%
Debt Instrument, Maturity Date	Jul. 01, 2019
Debt Instrument, Basis Spread on Variable Rate	0.61%
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 0.61%
Fair Value Hedges
Derivative [Line Items]
Current Notional Balance	$ 450,000
Lowest Possible Notional	450,000
Highest Possible Notional	$ 450,000
Lowest Interest Rate	2.375%
Highest Interest Rate	2.375%
Earliest Maturity Date	P2019Y0M0D
Latest Maturity Date	P2019Y0M0D
Forward Starting Swaps
Derivative [Line Items]
Current Notional Balance	$ 50,000
Lowest Possible Notional	50,000
Highest Possible Notional	$ 50,000
Lowest Interest Rate	2.50%
Highest Interest Rate	2.50%
Earliest Maturity Date	P2026Y0M0D
Latest Maturity Date	P2026Y0M0D