Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2010	Mar. 31, 2013 Performance Shares	Mar. 31, 2013 Restricted Stock Units	Mar. 31, 2013 Executive Officer Performance Shares	Sep. 30, 2012 Executive Officer Performance Shares	Mar. 31, 2013 Certain Employee Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, vesting period	4 years			7 years
Performance option awards		320,000	418,500			195,000	37,500	161,500
Performance options, vesting percentage upon initial public offering	25.00%
Performance options, vesting percentage upon achievement of revenue growth, growth rate	25.00%
Performance options, vesting percentage upon initial public offering and achieving consecutive growth rates	50.00%
Total unrecognized compensation cost related to unvested stock-based employee compensation arrangements	$ 10.4
Total unrecorded stock-based compensation cost, weighted- average period of recognition	3 years 8 months 5 days				3 years 4 months 13 days
Dividend yield	0.00%
Restricted stock units vesting percentage after one year	25.00%
Maximum percentage of performance-based restricted stock units	150.00%
Stock-based compensation expense related to restricted units	0.2
Unrecorded stock-based compensation cost	$ 7.6