Notes, Mortgage Notes and Other Debt Payable (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								3 Months Ended				3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 4.50% Notes [Member]	Dec. 31, 2012 4.50% Notes [Member]	Mar. 31, 2012 4.50% Notes [Member]	Apr. 11, 2011 4.50% Notes [Member]	Feb. 04, 2011 4.50% Notes [Member]	Mar. 30, 2004 4.50% Notes [Member]	Mar. 31, 2013 7.50% Notes [Member]	Dec. 31, 2012 7.50% Notes [Member]	Dec. 31, 2011 7.50% Notes [Member]	Jan. 31, 2011 7.50% Notes [Member]	Mar. 31, 2013 7.50% Senior Exchange Convertible Notes Member [Member]	Dec. 31, 2012 7.50% Senior Exchange Convertible Notes Member [Member]	Mar. 31, 2012 7.50% Senior Exchange Convertible Notes Member [Member]
Debt Instrument [Line Items]
Face amount of debt instrument								$ 120,000				$ 100,000
Outstanding debt			5,402	5,402		41,637	17,765		44,500	55,500,000			55,500	44,500
Stated interest rate (in hundredths)			4.50%		4.50%		4.50%				7.50%		7.50%		7.50%
Redemption price percentage (in hundredths)									100.00%				100.00%
Maturity Date of debt									Feb. 15, 2016
Repurchase amount of debt instrument							18,171
Debt Instrument, convertible, number of equity instruments (in shares)									33.3333				55.5555
Principal conversion standard base unit (in dollars per share)									$ 1.00				$ 1.00
Debt Instrument, Convertible, Conversion Price (in dollars per share)									$ 30.00				$ 18.00
Financial covenants: [Abstract]
Minimum cash and cash equivalents per financial covenants									20,000
Maximum indebtedness per financial covenants									150,000				33,000
Maximum indebtedness per financial covenants excluding for purposes of the covenant									50,000
Repurchase Right [Abstract]
Percentage of notes to be repurchased upon breach of financial covenants (in hundredths)									50.00%				50.00%
Repurchase price percentage upon breach of financial covenants (in hundredths)									110.00%				110.00%
Redemption right [Abstract]
Number of trading days the entity may redeem outstanding Notes									20 days
Number of consecutive trading days									30 days
Convertible conversion price percentage (in hundredths)									130.00%				130.00%
Principal amount of debt retired														44,500
Interest incurred	2,324	2,349
Interest capitalized	(551)	(112)
Interest expense	1,773	2,237
Interest payments	$ 3,935	$ 3,766