Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock Option Shares
Grants outstanding at beginning of the period	5,228,373	3,976,189	4,190,367	2,522,522
Granted	237,050	309,226	1,540,085	2,063,396
Exercised	(4,742)	(76,465)	(79,346)	(196,012)
Canceled or expired	(331,462)	(58,116)	(521,887)	(239,072)
Grants outstanding at end of the period	5,129,219	4,150,834	5,129,219	4,150,834
Grants exercisable at end of the period	1,859,285	891,157	1,859,285	891,157
Weighted Average Exercise Price
Grants outstanding at beginning of the period	$ 24.56	$ 21.82	$ 23.46	$ 11.76
Granted	$ 21.98	$ 39.17	$ 26.61	$ 34.86
Exercised	$ 8.85	$ 8.76	$ 11.69	$ 8.51
Canceled or expired	$ 21.19	$ 20.62	$ 22.63	$ 11.51
Grants outstanding at end of the period	$ 24.67	$ 23.37	$ 24.67	$ 23.37
Grants exercisable at end of the period	$ 18.61	$ 11.60	$ 18.61	$ 11.60