Notes Payable (Details) (USD $)	3 Months Ended		6 Months Ended							1 Months Ended	3 Months Ended	6 Months Ended			3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 4.50% Notes [Member]	Dec. 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]	Jul. 31, 2012 7.50% Notes [Member]	Jun. 30, 2013 7.50% Notes [Member]	Jun. 30, 2013 7.50% Notes [Member]	Dec. 31, 2012 7.50% Notes [Member]	Jan. 31, 2011 7.50% Notes [Member]	Jun. 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%
Outstanding debt					5,402,000	5,402,000	41,637,000	17,765,000			55,500,000	55,500,000	55,500,000		44,500,000	44,500,000
Repurchase amount of debt instrument								18,171,000
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
Principal amount of debt retired										44,500,000
Financial covenants: [Abstract]
Minimum cash and cash equivalents per financial covenants											20,000,000	20,000,000
Maximum indebtedness per financial covenants											150,000,000	150,000,000			33,000,000
Maximum indebtedness per financial covenants excluding for purposes of the covenant											50,000,000	50,000,000
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	2,326,000	2,334,000	4,650,000	4,683,000
Interest capitalized	(563,000)	(218,000)	(1,114,000)	(330,000)
Interest expense	1,763,000	2,116,000	3,536,000	4,353,000
Interest payments			$ 4,057,000	$ 3,898,000