Fair Value Disclosures (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Dec. 31, 2012
Mortgage notes and related accrued interest receivable	$ 468,557,000		$ 455,752,000
Investments in direct financing leases, net	235,302,000		234,089,000
Finance lease investment weighted average interest rate	12.02%
Minimum interest on investments in direct finance lease	11.93%
Maximum interest on investments in direct finance lease	12.38%
Long-term debt	1,383,392,000		1,368,832,000
Fixed Rate Mortgage Notes Receivable [Member]
Mortgage notes and related accrued interest receivable	468,600,000		455,800,000
Weighted average interest rate of mortgage notes receivable		8.98%	8.96%
Receivable interest rate minimum		7.00%	7.00%
Receivable interest rate maximum		11.31%	11.31%
Weighted market rate used for determining future cash flow for notes receivable	10.07%		10.07%
Fair value of notes receivable	445,600,000		431,200,000
Variable Rate Debt [Member]
Long-term debt	324,600,000		289,600,000
Long-term debt, weighted average interest rate	1.87%		1.88%
Variable Rate Converted to Fixed Rate [Member]
Long-term debt	240,000,000
Fixed Rate Debt [Member]
Long-term debt	1,060,000,000		1,080,000,000
Long-term debt, weighted average interest rate	6.36%		6.35%
Weighted market rate for determining fair value of debt	3.83%		4.46%
Fair value of debt	1,180,000,000
Long-term Debt, Fair Value			$ 1,170,000,000
Minimum [Member] | Fixed Rate Mortgage Notes Receivable [Member]
market rate used as discount factor to determine fair value of notes	9.00%		9.00%
Minimum [Member] | Fixed Rate Debt [Member]
market rate used as discount factor to determine fair value of debt	2.89%		3.41%
Maximum [Member] | Fixed Rate Mortgage Notes Receivable [Member]
market rate used as discount factor to determine fair value of notes	11.31%		11.31%
Maximum [Member] | Fixed Rate Debt [Member]
market rate used as discount factor to determine fair value of debt	4.39%		5.17%