Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Amount of prepaid tax amortized to income tax expense	$ 153,498
Deferred tax assets valuation allowance increase (decrease)	61,200,000	80,800,000	(70,500,000)
Interest expense	84,000	65,000
Increase in liability for uncertain tax positions	25,000,000
Tax benefit that would be recognized if unrecognized tax benefits were realized and not subject to valuation allowances	21,200,000
Federal
Income Taxes [Line Items]
Net operating loss carryforwards related to stock-based compensation tax deductions	$ 35,000,000