Summary of Stock Options Outstanding (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Number of Shares
Outstanding at January 1, 2015 | shares	21,541,664
Granted | shares	1,541,100
Exercised | shares	(1,700,964)
Forfeited | shares	(706,387)
Expired | shares	(896,184)
Outstanding at December 31, 2015 | shares	19,779,229
Vested and expected to vest at December 31, 2015 | shares	19,597,097
Exercisable at December 31, 2015 | shares	17,217,332
Weighted Average Exercise Price per Share
Outstanding at January 1, 2015 | $ / shares	$ 4.53
Granted | $ / shares	4.11
Exercised | $ / shares	1.91
Forfeited | $ / shares	5.78
Expired | $ / shares	7.70
Outstanding at December 31, 2015 | $ / shares	4.54
Vested and expected to vest at December 31, 2015 | $ / shares	4.53
Exercisable at December 31, 2015 | $ / shares	$ 4.47
Aggregate Intrinsic Value
Outstanding at January 1, 2015 | $	$ 33,495
Outstanding at December 31, 2015 | $
Vested and expected to vest at December 31, 2015 | $	0
Exercisable at December 31, 2015 | $	$ 0