Sale of Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			0 Months Ended		1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 25, 2013 Underwritten Public Offering [Member] Common Stock [Member]	Apr. 03, 2013 Underwritten Public Offering [Member] Common Stock [Member]	Apr. 29, 2013 Underwritten Public Offering [Member] Common Stock [Member]
Class of Stock [Line Items]
Common stock issued, shares					1,321,000
Common stock, par value	$ 0.521	$ 0.521			$ 0.521
Public offering price per share					$ 26.50
Share price to underwriters					$ 25.44
Length of option period to purchase overallotment of shares					30 days
Shares included in overallotment option					198,150
Shares issued upon exercise of overallotment option				100,000
Issuance of common stock, net of issuance costs	$ 35,894	$ 0	$ 0			$ 35,894