Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of quarterly results
Revenue	$ 20,091	$ 19,942	$ 17,003	$ 10,207	$ 19,365	$ 33,637	$ 43,028	$ 37,970	$ 67,243	$ 134,000	$ 77,362
Gross profit (loss)	912	2,445	11	(3,408)	2,339	16,121	27,200	23,975	(40)	69,635	41,157
Income (loss) from operations	(2,151)	(1,141)	(3,098)	(6,646)	(723)	11,885	23,339	20,250	(13,036)	54,751	28,694
Income (loss) before income taxes	(2,085)	(844)	(3,386)	(6,271)	(876)	11,775	23,403	20,331	(12,586)	54,633	29,040
Net income (loss)	$ (1,131)	$ 272	$ (1,312)	$ (3,367)	$ 861	$ 8,186	$ 9,908	$ 19,104	$ (5,538)	$ 38,059	$ 29,111
Basic income (loss) per common share	$ (0.05)	$ 0.01	$ (0.06)	$ (0.15)	$ 0.04	$ 0.36	$ 0.43	$ 0.83	$ (0.25)	$ 1.67	$ 1.34
Diluted income (loss) per common share	$ (0.05)	$ 0.01	$ (0.06)	$ (0.15)	$ 0.04	$ 0.35	$ 0.41	$ 0.80	$ (0.25)	$ 1.61	$ 1.28
Weighted average common shares outstanding used in computing net income per common share:
Basic	22,538,292	22,524,611	22,518,364	22,514,539	22,561,883	22,822,286	23,031,039	22,993,614	22,523,951	22,852,205	21,726,090
Diluted	22,538,292	23,050,618	22,518,364	22,514,539	23,102,072	23,410,525	23,928,408	23,943,644	22,523,951	23,596,162	22,790,896