Assumptions Used for Calculating Fair Values of Stock Option Awards (Detail) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 1999	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Options Granted
Weighted average grant date fair value, per share		$ 26.46	$ 19.84	$ 17.35
Weighted average assumptions used:
Expected volatility		52.80%	66.40%	73.50%
Expected lives	3 years	5 years 0 months 0 days	4 years 10 months 24 days	4 years 8 months 12 days
Risk-free interest rates		1.70%	0.70%	0.80%
Dividends yields		0.00%	0.00%	0.00%