Employee Savings Plan - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Minimum age to be eligible to defined contribution plan	21 years
Maximum contribution by company expressed, per dollar of employee contributions	$ 0.5
Maximum contribution by company expressed as percentage of employee pre-tax salary	25.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%
Company contributions vest at end of two years	20.00%
Company contributions vest at end of three years	40.00%
Company contributions vest at end of four years	60.00%
Company contributions vest at end of five years	100.00%
Company contributions to employee savings plan	$ 1,555,000	$ 1,423,000	$ 1,362,000