Stock-based Compensation - Market-based Stock Options and RSUs - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2011 Market-based RSUs [Member]	Dec. 31, 2009 Market-based RSUs [Member]	Dec. 31, 2009 Market-based stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs granted during the period		90,000	98,000
Estimated grant date fair value of restricted stock		$ 1.1	$ 0.9
Average derived service period, in years		3 years 11 months 5 days	4 years 4 months 6 days	4 years 10 months 17 days
Risk-free interest rate		2.90%	3.50%	3.10%
Implied volatility		40.00%	50.00%	50.00%
RSUs that remain outstanding		0	0	0
Options granted during the period				294,076
Estimated grant date fair value of stock options				$ 1.7
RSUs vested			78,000
Stock options vested				190,716