Summary of Significant Accounting Policies - Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net income	$ 1,898	$ 129,705	$ 3,063	$ 102,561
Other comprehensive income:
Realized gains on marketable securities reclassified to gain on sale of marketable securities, net of a benefit from income taxes of $2,757				(5,120)
Unrealized gains on marketable securities, net of provision for income taxes of $377				702
Total comprehensive income	$ 1,898	$ 129,705	$ 3,063	$ 98,143