Debt (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Short-term debt:
Bank Credit Facility		$ 113,000	$ 38,000
Long-term debt, current and noncurrent:
Long-term debt		124,979	199,939
Total	[1]	237,979	237,939
Senior Notes 2015 [Member] | Senior Note 6.05 % [Member]
Long-term debt, current and noncurrent:
Long-term debt	[1]	0	74,989
Senior Notes 2016 [Member] | Senior Note 6.85 % [Member]
Long-term debt, current and noncurrent:
Long-term debt	[1]	$ 124,979	$ 124,950

[1] The Company designates debt obligations as "long-term” based on maturity date at issuance.