Long-Term Debt (Details) (USD $)	12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2011 3.75 % senior unsecured notes due September 1, 2016	Dec. 31, 2013 Long-term Debt [Member]
Debt Instrument [Line Items]
Unsecured notes	$ 250,000,000	$ 250,000,000
Long-term Debt, Gross	138,750,000	0
Unamortized issuance costs	(1,222,000)	(1,681,000)
Long-term Debt	387,528,000	248,319,000
Current portion, long-term debt	15,000,000	0
Long-term Debt, Excluding Current Maturities	372,528,000	248,319,000
Senior unsecured notes, issued amount			250,000,000
Senior unsecured notes, interest rate			3.75%
Senior unsecured notes, maturity date			Sep. 01, 2016	Apr. 05, 2019
Senior unsecured notes, proceeds			247,700,000
Senior unsecured notes, term	5 years		5 years
Senior unsecured notes, interest payments	quarterly		semiannually
Senior unsecured notes, interest payment dates			March 1 and September 1
Debt Instrument, Periodic Payment, Principal				$ 3,750,000
Debt Instrument, Description of Variable Rate Basis				Interest is accrued at a one-month LIBOR rate