Line of Credit (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Line of Credit Facility [Line Items]
Borrowings under line of credit	$ 35,000,000
U.S. Bank and East-West Bank [Member] | Revolving Credit Facility [Member] | Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	100,000,000
Rent adjusted fixed charge coverage ratio	2.50
Balance sheet leverage ratio	0.76
Minimum requirement of unrestricted cash, cash equivalents, and publicly traded marketable securities	40,000,000
Borrowings under line of credit	35,000,000
Line of credit, amount outstanding	$ 0
U.S. Bank and East-West Bank [Member] | Revolving Credit Facility [Member] | Unsecured Debt [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Rent adjusted fixed charge coverage ratio	1.50
U.S. Bank and East-West Bank [Member] | Revolving Credit Facility [Member] | Unsecured Debt [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Balance sheet leverage ratio	1.50
U.S. Bank and East-West Bank [Member] | Revolving Credit Facility [Member] | Unsecured Debt [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.75%