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Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, Minimum	0.58%	0.66%	1.35%
Risk free interest rate, Maximum	0.83%	2.17%	1.83%
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	53.00%	53.90%	55.20%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected lives	3 years 9 months 18 days	3 years 6 months	3 years 7 months 6 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected lives	4 years 7 months 6 days	4 years 6 months	4 years 3 months 18 days

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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