Debt and Credit Agreements (Details 2) - Revolving credit facility - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 425,000		$ 425,000		$ 140,000
Long-term debt, weighted average interest rate	2.10%		2.10%
Availability under the credit facility	$ 1,400,000		$ 1,400,000
Weighted-average effective interest rate	2.10%	2.20%	2.20%	2.20%