Long-term Debt - Narrative (Details) (USD $)	12 Months Ended			0 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 05, 2011 Revolving credit facility [Member]	Dec. 31, 2012 Revolving credit facility [Member]	Dec. 31, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member]	Dec. 31, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member] Minimum [Member]	Dec. 31, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member] Maximum [Member]
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity					$ 200,000,000
Revolving credit facility, potentially additional borrowing capacity					100,000,000
Debt instrument, description of variable rate basis						LIBOR or CDOR
Revolving credit facility, margin added to variable interest rate							1.75%	2.25%
Revolving credit facility, amendment fees				700,000
Revolving credit facility, average borrowings	26,300,000	21,100,000
Revolving credit facility, minimum amount borrowed	0	0
Revolving credit facility, maximum amount borrowed	91,500,000	89,500,000
Revolving credit facility, weighted-average interest rate	2.10%	2.20%
Total unused facility fees and letter of credit participation fees	900,000	1,300,000	1,800,000
Unamortized debt issuance costs	$ 1,500,000	$ 1,900,000