Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income (loss)	$ (21,598)	$ 49,762	$ (39,741)	$ 36,636
Noncumulative dividends on convertible preferred stock		(6,332)		(12,664)
Undistributed earnings allocated to participating securities		(41,111)		(22,715)
Net income (loss) attributable to common stockholders, basic	(21,598)	2,319	(39,741)	1,257
Adjustment to undistributed earnings allocated to participating securities		995		559
Net income (loss) attributable to common stockholders, diluted	$ (21,598)	$ 3,314	$ (39,741)	$ 1,816
Basic shares:
Weighted average common shares outstanding	14,681,570	1,355,934	8,078,308	1,329,133
Shares used to compute net income (loss) per share attributable to common stockholders:
Weighted average common shares outstanding	14,681,570	1,355,934	8,078,308	1,329,133
Weighted average effect of dilutive stock options		629,710		639,688
Weighted average number of shares outstanding, Diluted shares	14,681,570	1,985,644	8,078,308	1,968,821
Net income (loss) per share attributable to common stockholders:
Basic	$ (1.47)	$ 1.71	$ (4.92)	$ 0.95
Diluted	$ (1.47)	$ 1.67	$ (4.92)	$ 0.92