Trust Preferred Securities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Trust Preferred Securities Textual [Abstract]
Trust preferred securities, Description	On September 15, 2005, RST II, a wholly-owned subsidiary of the Company, closed a pooled private offering of 10,000 Capital Securities with a liquidation amount of $1,000 per security. The proceeds of the offering were loaned to the Company in exchange for junior subordinated debentures with terms similar to the Capital Securities. Distributions on the Capital Securities are payable quarterly at a variable rate that is based upon the 3-month LIBOR plus 1.80 percent and are included in interest expense in the consolidated financial statements. These securities may be included in Tier 1 capital (with certain limitations applicable) under current regulatory guidelines and interpretations.
Capital Securities	$ 10.3	$ 10.3
Capital securities maturity date	Sep. 15, 2035

Date of maturity of a security categorized as held-to-maturity, in CCYY-MM-DD format.

No definition available.

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