Revolving Credit Facility (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Revolving Credit Facility [Abstract]
Term of revolving credit facility (in years)	4Y
Line of credit facility	$ 100
Maximum borrowing capacity	$ 150
Percentage of subsidiary stock securing debt (in hundredths)	65.00%
Unused commitment fee on the average daily unused portion (in hundredths)	0.25%
LIBOR Borrowings [Member]
Line of Credit Facility [Line Items]
Description of basis for variable rate	LIBOR
Applicable margin on variable rate on borrowings, minimum (in hundredths)	2.00%
Applicable margin on variable rate on borrowings, maximum (in hundredths)	2.75%
Alternate Base Rate Borrowings [Member]
Line of Credit Facility [Line Items]
Description of basis for variable rate	alternate base rate
Applicable margin on variable rate on borrowings, minimum (in hundredths)	0.00%
Applicable margin on variable rate on borrowings, maximum (in hundredths)	0.75%
Alternate base rates, applicable margins [Abstract]
Applicable margin, federal funds rate (in hundredths)	0.50%
Applicable margin, 30-day LIBOR (in hundredths)	2.00%