Notes Payable (Details Textual) (USD $)	6 Months Ended
	Jun. 30, 2012
Unsecured Revolving Credit Facility Before Amendment [Member]
Notes Payable (Textual) [Abstract]
Unsecured Revolving credit facility	$ 350,000,000
Unsecured Revolving Credit Facility After Amended [Member]
Notes Payable (Textual) [Abstract]
Revolving credit facility before amended	Jun. 15, 2017
Unsecured Revolving credit facility	420,000,000
Line of Credit Facility Covenants Tangible Net Worth Description	Permit the Tangible Net Worth (as defined in the Amended Credit Facility) as of the end of any fiscal quarter of the Company to be less than the sum of (i) $246,103,400 plus (ii) 25% of the Company’s Consolidated Net Income (as defined in the Amended Credit Facility) (but only if a positive number) for each fiscal quarter ended subsequent to December 31, 2011 plus (iii) 90% of the net cash proceeds from the issuance of the Company’s capital stock after December 31, 2011
Line of Credit Facility Covenants Aggregate Fixed Charge Coverage Ratio Period	4 years
Tangible net worth Sum	246,103,400
Consolidated Net Income	0.25
Net Cash Proceeds from issuance of Capital Stock	0.90
Revolving credit facility capacity Period after amendment	5 years
Revolving Enhanced Borrowing	450,000,000
Line of Credit Facility Additional Capacity Available	30,000,000
Letter of Credit [Member]
Notes Payable (Textual) [Abstract]
Revolving credit facility before amended	Jun. 15, 2017
Unsecured Revolving credit facility	25,000,000
Credit facility, current	5,000,000
Credit facility, maximum	10,000,000
Swingline Loans [Member]
Notes Payable (Textual) [Abstract]
Unsecured Revolving credit facility	$ 10,000,000
Maximum [Member] | Unsecured Revolving Credit Facility After Amended [Member]
Notes Payable (Textual) [Abstract]
Line of Credit Facility covenants aggregate Fixed Charge Coverage Ratio	2.5
Consolidated Leverage Ratio	2.75
Minimum [Member] | Unsecured Revolving Credit Facility After Amended [Member]
Notes Payable (Textual) [Abstract]
Line of Credit Facility covenants aggregate Fixed Charge Coverage Ratio	1.00
Consolidated Leverage Ratio	1.00