Debt - Additional Information (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) $ / shares	Mar. 31, 2015 USD ($) shares	Dec. 31, 2010 USD ($)	Dec. 31, 2007 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Percent of notes required to be repurchased at the option of the holders			100.00%
Converted debt, shares issued (in shares) | shares		90,957
Debt satisfaction charges, net	$ 162,000	$ (10,375,000)
Mortgages and Notes Payable [Member]
Debt Instrument [Line Items]
Weighted average interest rate	4.90%				4.90%
6% Convertible Guaranteed Note [Member]
Debt Instrument [Line Items]
Stated interest rate	6.00%				6.00%
Face amount of debt instrument	$ 12,400,000		$ 115,000,000		$ 12,400,000
Maturity date	Jan. 31, 2030
Conversion ratio numerator	156.5514
Conversion price (dollars per share) | $ / shares	$ 6.39
Debt satisfaction charges, net		77,000
6.804% Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Stated interest rate				6.804%
Face amount of debt instrument				$ 200,000,000
Principal amount outstanding	$ 129,120,000				129,120,000
Unamortized debt issuance costs	2,099,000				$ 2,124,000
6.804% Trust Preferred Securities [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				1.70%
Other Debt Obligations [Member]
Debt Instrument [Line Items]
Debt satisfaction charges, net		(14,000)
Unsecured Credit Agreement [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	905,000,000
Maximum borrowing capacity with lender approval	$ 1,810,000,000
Convertible Debt [Member]
Debt Instrument [Line Items]
Amount of debt converted		$ 600,000
Minimum [Member] | Mortgages and Notes Payable [Member]
Debt Instrument [Line Items]
Stated interest rate	2.20%				2.20%
Maximum [Member] | Mortgages and Notes Payable [Member]
Debt Instrument [Line Items]
Stated interest rate	7.80%				7.80%