Notes Payable (Details) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended
	Oct. 26, 2012	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2011	Oct. 26, 2012 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2012 Unsecured Debt [Member]	Dec. 31, 2012 Long-term Debt [Member]	Dec. 31, 2012 Agreement [Member]	Dec. 31, 2012 Federal Funds Rate [Member]	Dec. 31, 2011 Lender S Prime Rate [Member]	Dec. 31, 2011 Eurodollar Rate [Member]	Dec. 31, 2011 British Bankers Association S Libor Rate [Member]	Dec. 31, 2012 Great Lakes Advisors [Member]
Debt Instrument [Line Items]
Notes payable						$ 0
Notes payable outstanding		2,093,000		52,822,000			1,100,000	1,000,000
Interest rate on loan agreement							1.25%		4.00%
Loan agreement with unaffiliated banks, amount		$ 101,000,000			$ 75,000,000	$ 100,000,000		$ 1,000,000
Maturity date			Dec. 15, 2013		Oct. 26, 2012	Oct. 25, 2013	Sep. 30, 2014	Jun. 01, 2015
Amendment Date	Oct. 26, 2012
Interest rate basis points on borrowings		4.00%								1.00%	0.50%	1.50%	3.00%	1.00%
Percentage of commitment fee payment		0.50%