Long-Term Debt (Detail Textuals) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Aug. 31, 2010
Line of Credit Facility [Line Items]
Percentage of ownership			100.00%
Maximum amount outstanding during the period		$ 350,000,000
Line of credit facility expiration period	5 years
Description of variable rate basis of debt instrument	The Base Rate, which is the highest of Bank of America's "prime rate" for the day of the borrowing, a fluctuating rate per annum equal to the Federal Funds Rate plus 0.50%, and a rate per annum equal to the one (1) month LIBOR rate plus 1.00%, in each case plus a margin that ranges from 0.25% to 1.25% based on a quarterly debt covenant calculation; or
Credit facility
Line of Credit Facility [Line Items]
Outstanding borrowings under the facility	107,000,000	203,300,000	200,000,000
Maximum amount outstanding during the period		50,000,000
Revolving credit facility
Line of Credit Facility [Line Items]
Outstanding borrowings under the facility			350,000,000
Origination fees and other costs		2,300,000
Letter of swingline subfacility
Line of Credit Facility [Line Items]
Maximum amount outstanding during the period		$ 25,000,000