Credit Arrangements (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt payable non-affiliates	$ 97,000	$ 97,000
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Debt Instrument [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 1,000.00
Preferred stock, shares outstanding	97,000
Senior Notes, unaffiliated [Member]
Debt Instrument [Line Items]
Long-term debt payable non-affiliates	$ 97,000
Capital trust equity [Member]
Debt Instrument [Line Items]
Long-term debt payable non-affiliates	3,000
5% Subordinated Deferrable Interest Notes, due June 30, 2047 [Member]
Debt Instrument [Line Items]
Long-term debt payable non-affiliates	100,000
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Debt Instrument [Line Items]
Long-term debt payable non-affiliates	$ 97,000