Supplementary Quarterly Financial Data (Unaudited) - Consolidated Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended					12 Months Ended			3 Months Ended			6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012 As Reported [Member]	Jun. 30, 2012 As Reported [Member]	Mar. 31, 2012 As Reported [Member]	Jun. 30, 2012 As Reported [Member]	Sep. 30, 2012 As Reported [Member]	Sep. 30, 2012 Adjustments [Member]	Jun. 30, 2012 Adjustments [Member]	Mar. 31, 2012 Adjustments [Member]	Jun. 30, 2012 Adjustments [Member]	Sep. 30, 2012 Adjustments [Member]	Sep. 30, 2012 As Restated [Member]	Jun. 30, 2012 As Restated [Member]	Mar. 31, 2012 As Restated [Member]	Jun. 30, 2012 As Restated [Member]	Sep. 30, 2012 As Restated [Member]
Net loss	$ (78,151)	$ (41,134)	$ 1,309	$ 3,949	$ 2,404	$ (100,060)	$ (33,472)	$ (19,586)	$ (25,988)	$ (10,304)	$ 6,859	$ (3,445)	$ (29,433)	$ (4,461)	$ 17,469	$ (5,484)	$ 11,985	$ 7,524	$ (30,449)	$ 7,165	$ 1,375	$ 8,540	$ (21,909)
Reclassified to earnings, net of provision for (benefit from) income taxes of $-, $161, $161, $-, $-, $-, $-, $-, $- and $-, $161, $161																(298)		(298)			(298)		(298)
Unrealized hedging gains, net of provision for (benefit from) income taxes of $3,578, ($3,578), $-, ($12,087), $12,087, $-, $3,889, ($3,889), $- and ($4,620), $4,620, $-						(298)	298		(7,223)	22,448	(6,645)		8,580	7,223	(22,448)	6,645		(8,580)
Net change in unrealized gains and losses on marketable securities, net of benefit from (provision for) income taxes of $6,793, $-, $6,793, $682, $-, $682, $46, $-, $46 and $7,520, $-, $7,520						(15,760)	(12,152)	1,711	(86)	(1,268)	(12,612)		(13,966)						(86)	(1,268)	(12,612)		(13,966)
Other comprehensive income (loss)						(16,058)	(11,854)	1,711	(7,309)	21,180	(19,257)		(5,386)	7,223	(22,448)	6,347		(8,878)	(86)	(1,268)	(12,910)		(14,264)
Comprehensive income (loss)						$ (116,118)	$ (45,326)	$ (17,875)	$ (33,297)	$ 10,876	$ (12,398)		$ (34,819)	$ 2,762	$ (4,979)	$ 863		$ (1,354)	$ (30,535)	$ 5,897	$ (11,535)		$ (36,173)