Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Short-term debt:
Bank Credit Facility, expires October 6, 2015	$ 38,000	$ 38,000
Long-term debt:
Long-term debt	199,890	199,874
Total	237,890	237,874
Senior Notes 2015 [Member] | Senior Note 6.05 % [Member]
Long-term debt:
Long-term debt	74,969	74,962
Senior Notes 2016 [Member] | Senior Note 6.85 % [Member]
Long-term debt:
Long-term debt	$ 124,921	$ 124,912