Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Option Shares
Grants outstanding at beginning of the period	4,190,367	2,522,522	2,417,659
Granted	1,694,560	2,283,719	1,269,470
Exercised	(86,007)	(241,056)	(371,353)
Canceled or expired	(582,717)	(371,818)	(793,254)
Grants outstanding at end of the period	5,216,203	4,190,367	2,522,522
Grants exercisable at end of the period	2,019,514	1,051,329	615,394
Grants vested and expected to vest at end of the period	4,462,100	3,467,069	2,343,086
Weighted Average Exercise Price
Grants outstanding at beginning of the period	$ 23.46	$ 11.76	$ 11.18
Granted	$ 25.67	$ 34.18	$ 12.92
Exercised	$ 11.40	$ 11.31	$ 10.18
Canceled or expired	$ 22.79	$ 16.83	$ 12.59
Grants outstanding at end of the period	$ 24.45	$ 23.46	$ 11.76
Grants exercisable at end of the period	$ 18.69	$ 11.91	$ 12.71
Grants vested and expected to vest at end of the period	$ 23.27	$ 21.50	$ 11.73
Aggregate Intrinsic Value
Outstanding at end of year	$ 7,794
Vested and expected to vest	5,973
Exercisable at end of year	$ 7,671
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	8 years 15 days
Vested and expected to vest	7 years 15 days
Exercisable at end of year	7 years 11 months 19 days