Long-Term Debt Long-Term Debt (Details) (USD $)			1 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Aug. 31, 2011 3.75 % senior unsecured notes due September 1, 2016
Debt Instrument [Line Items]
Unsecured notes	$ 250,000,000	$ 250,000,000
Unamortized issuance costs	(1,910,000)	(2,139,000)
Total long-term debt	248,090,000	247,861,000
Senior unsecured notes, issued amount			250,000,000
Senior unsecured notes, interest rate			3.75%
Senior unsecured notes, maturity date			Sep. 01, 2016
Senior unsecured notes, proceeds			$ 247,700,000
Senior unsecured notes, term (in years)			5 years
Senior unsecured notes, interest payments			semiannually
Senior unsecured notes, interest payment dates			March 1 and September 1