Debt Obligations (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Debt [Abstract]
Long-term notes payable	$ 314,844,000	$ 350,000,000
Less current portion of long-term debt	(19,688,000)	(17,500,000)
Long-term debt	295,156,000	332,500,000
Scheduled maturities of long-term debt [Abstract]
2013	19,688,000
2014	52,500,000
2015	87,500,000
2016	135,468,000
Total	295,156,000	332,500,000
Line of credit facility [Abstract]
Term of credit facility (in years)	5Y
Advance from unsecured resolving credit facility	175,000,000
Maximum borrowing capacity under term loan	350,000,000
Maturity of Bank Facility	November 30, 2016
Line of Credit Facility, Interest Rate Description	Borrowings under the Bank Facility bear interest, at the Company's option, at either (A) the highest of (i) the Prime Rate, (ii) the Federal Funds Effective Rate plus 0.5%, and (iii) the Adjusted LIBO Rate for an Interest Period of one month plus 1.0%, in each case plus an Applicable Margin based on the Company's Leverage Ratio or (B) the interest rate equal to (i) the rate for US dollar deposits in the London interbank market for such Interest Period multiplied by (ii) the Statutory Reserve Rate, plus (iii) the Applicable Margin.
Minimum Unused Commitment Fee	0.25%
Maximum Unused Commitment Fee	0.50%
Outstanding term loan	314,800,000
Outstanding letters of credit	15,100,000
Interest rate (in hundredths)	3.00%
Interest expense paid	3,300,000
Available borrowing capacity under unsecured revolving line of credit	159,900,000
Issuance Of Equity Disclosure [Abstract]
Stock Issued in Initial Public Offering (in shares)	2,875,000
Proceeds from equity offering	217,565,000
Proceeds From Issuance Initial Public Offering Used For Repayment Of Debt	$ 30,800,000