Notes Payable (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended							1 Months Ended	3 Months Ended	9 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2007	Sep. 30, 2013 4.50% Notes [Member]	Dec. 31, 2012 4.50% Notes [Member]	Apr. 02, 2011 4.50% Notes [Member]	Feb. 04, 2011 4.50% Notes [Member]	Dec. 31, 2009 4.50% Notes [Member]	Oct. 17, 2008 4.50% Notes [Member]	Mar. 30, 2004 4.50% Notes [Member]	Jul. 31, 2012 7.50% Notes [Member]	Sep. 30, 2013 7.50% Notes [Member]	Sep. 30, 2013 7.50% Notes [Member]	Dec. 31, 2012 7.50% Notes [Member]	Feb. 04, 2011 7.50% Notes [Member]	Sep. 30, 2013 7.50% Senior Exchange Convertible Notes Member [Member]	Dec. 31, 2012 7.50% Senior Exchange Convertible Notes Member [Member]	Jul. 31, 2012 7.50% Senior Exchange Convertible Notes Member [Member]
Debt Instrument [Line Items]
Face amount of debt instrument												$ 120,000,000					$ 100,000,000			$ 44,500,000
Stated interest rate (percent)						4.50%						4.50%	7.50%	7.50%	7.50%			7.50%		7.50%
Redemption price percentage (percent)						100.00%									100.00%
Effective interest rate (percent)	7.50%		7.50%
Outstanding debt					5,200,000	5,402,000	5,402,000	41,637,000	17,765,000	14,076,000	35,920,000			55,500,000	55,500,000	55,500,000		44,500,000	44,500,000
Repurchase amount of debt instrument					4,857,000				18,171,000	11,696,000	28,112,000
Debt Instrument, convertible, number of equity instruments (in shares)														33.3333				55.5555
Principal conversion standard base unit (in dollars per share)														$ 30.00	$ 30.00			$ 18.00
Minimum cash and cash equivalents per financial covenants														20,000,000	20,000,000
Principal amount of debt retired													44,500,000
Financial covenants: [Abstract]
Maximum indebtedness per financial covenants																		33,000,000
Repurchase Right [Abstract]
Percentage of notes to be repurchased upon breach of financial covenants (percent)																		50.00%
Repurchase price percentage upon breach of financial covenants (percent)															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%
Interest incurred	2,324,000	2,229,000	6,974,000	6,912,000
Interest capitalized	(3,344,000)	(326,000)	(4,459,000)	(656,000)
Interest expense	(1,020,000)	1,903,000	2,515,000	6,256,000
Interest payments			$ 7,807,000	$ 7,473,000