Summary of Significant Accounting Policies - Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended					12 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
Net loss	$ (78,151)	$ (41,134)	$ 1,309	$ 3,949	$ 2,404	$ (100,060)	$ (33,472)	$ (19,586)
Other comprehensive income (loss):
Realized gains on marketable securities reclassified to earnings, net of provision for income taxes of ($5,785) in 2010, ($12,291) in 2011 and ($9,318) in 2012						(17,303)	(22,827)	(10,744)
Unrealized hedging gains, net of provision for (benefit from) income taxes of $161 in 2011 and ($161) in 2012						(298)	298
Unrealized gains on marketable securities, net of provision for income taxes of $6,707 in 2010, $5,748 in 2011 and $831 in 2012						1,543	10,675	12,455
Comprehensive loss						$ (116,118)	$ (45,326)	$ (17,875)