Employee Benefit Plan - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Participants contribution	$ 17,500
Employer contribution	2.00%
Employer contribution	20.00%
Initial vesting period of employer contribution	2 years
Full vesting period of employer contribution	6 years
Contribution expenses	$ 4,700,000	$ 3,700,000	$ 1,700,000