Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Option Shares
Outstanding Beginning of year	2,417,659	1,415,009	1,488,802
Granted	1,269,470	1,595,375	601,228
Exercised	(371,353)	(25,291)	(283,605)
Canceled or expired	(793,254)	(567,434)	(391,416)
Outstanding at end of year	2,522,522	2,417,659	1,415,009
Exercisable at end of year	615,394	742,211	653,253
Vested and expected to vest	2,343,086
Weighted Average Exercise Price
Outstanding at Beginning of year	$ 11.18	$ 12.84	$ 16.74
Granted	$ 12.92	$ 9.18	$ 9.48
Exercised	$ 10.18	$ 6.54	$ 7.08
Canceled or expired	$ 12.59	$ 9.90	$ 26.52
Outstanding at end of year	$ 11.76	$ 11.18	$ 12.84
Exercisable at end of year	$ 12.71	$ 15.60	$ 17.58
Vested and expected to vest	$ 11.73
Aggregate Intrinsic Value
Outstanding at end of year	$ 36,252,000
Exercisable at end of year	8,870,000
Vested and expected to vest	$ 33,792,000
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	8 years 7 months 6 days
Exercisable at end of year	6 years 10 months 24 days
Vested and expected to vest	8 years 7 months 6 days