Debt Obligations (Details Textuals 1) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Jun. 30, 2011 Research Office Center [Member]	Sep. 30, 2011 Concord Airport Plaza [Member]
Debt Instrument [Line Items]
Unamortized fixed-rate debt premium						$ 300,000	$ 200,000
Debt obligations (Additional) (Textuals)
Repurchased outstanding unsecured notes			24,319,000
Variable interest rate on outstanding balance	LIBOR plus 0.725%		LIBOR plus 0.725%
Long-term Debt, Gross	59,800,000		59,800,000		59,800,000
Less: unamortized exchangeable debt discount	100,000		100,000		900,000
Contractual coupon interest recognized on exchangeable debt	600,000	700,000	1,700,000	2,600,000
Interest on amortization of debt discount	300,000	300,000	800,000	1,300,000
Debt discount write-offs resulting from debt repurchases	$ 0	$ 0	$ 0	$ 1,600,000