Notes Payable (Details) (USD $)	12 Months Ended					12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2011	Dec. 31, 2010	Dec. 31, 2013 4.50% Notes [Member]	Dec. 31, 2012 4.50% Notes [Member]	Mar. 30, 2004 4.50% Notes [Member]	Jul. 31, 2012 7.50% Notes [Member]	Dec. 31, 2013 7.50% Notes [Member] D	Dec. 31, 2012 7.50% Notes [Member]	Feb. 04, 2011 7.50% Notes [Member]	Feb. 15, 2014 7.50% Notes [Member] Subsequent Event [Member]	Dec. 31, 2013 7.50% Senior Exchange Convertible Notes Member [Member]	Jul. 31, 2012 7.50% Senior Exchange Convertible Notes Member [Member]	Dec. 31, 2013 7.5% Senior Exchange Convertible Notes [Member]	Dec. 31, 2012 7.5% Senior Exchange Convertible Notes [Member]	Dec. 31, 2013 Minimum [Member] 7.50% Notes [Member]
Debt Instrument [Line Items]
Outstanding debt			$ 114,598,000			$ 5,402,000	$ 5,402,000			$ 55,500,000	$ 55,500,000			$ 44,500,000		$ 44,500,000	$ 44,500,000
Long-term Debt	105,402,000	105,402,000
Face amount of debt instrument								120,000,000				100,000,000		44,500,000
Stated interest rate (percent)								4.50%	7.50%			7.50%			7.50%
Write off of deferred costs									1,144,000
Repurchase amount of debt instrument			104,473,000										19,000
Redemption price percentage (percent)						100.00%				100.00%
Effective interest rate (percent)	7.50%
Financial covenants: [Abstract]
Minimum cash and cash equivalents	144,727,000	79,815,000	124,316,000		115,502,000													20,000,000
Convertible, number of equity instruments (in shares)										33.3333				55.5555
Principal conversion standard base unit (in dollars per share)										$ 1				$ 1,000
Convertible conversion price (in dollars per share)										$ 30.00				$ 18.00
Repurchase Right [Abstract]
Percentage of notes to be repurchased upon breach of financial covenants (percent)										50.00%				50.00%
Repurchase price percentage upon breach of financial covenants (percent)										110.00%				110.00%
Interest payments	7,929,000	7,587,000	6,136,000
Percentage of face value the notes were sold to the public				100.00%
Redemption right [Abstract]
Number of trading days the entity may redeem outstanding Notes										20
Number of consecutive trading days										30 days
Convertible conversion price percentage (in hundredths)										130.00%				130.00%
Principal amount of debt retired									44,500,000
Maturities of notes payable:
2014	0
2015	0
2016	100,000,000
2017	0
2018	0
Thereafter	5,402,000
Total Corporate	105,402,000
Interest Costs Incurred
Interest incurred	9,296,000	9,236,000	9,955,000
Interest capitalized	(6,466,000)	(1,263,000)	(439,000)
Interest expense	$ 2,830,000	$ 7,973,000	$ 9,516,000