Income Taxes - Schedule of Reconciliation between Statutory Income Tax Rate and Company's Effective Income Tax (Benefit) Provision Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax rate at federal statutory rates	35.00%	35.00%	35.00%
Federal net operating loss and tax credit adjustments		24.40%	(0.68%)
State taxes, net of federal benefit	2.02%	(58.42%)	0.56%
State net operating loss revaluation	(0.15%)	(19.74%)	(2.51%)
Nondeductible equity-based compensation	(1.01%)	(275.10%)	0.15%
Tax credits	0.25%	21.17%	(1.73%)
Nondeductible expenses	(0.15%)	(17.15%)	0.53%
Charitable contribution carryforward valuation allowance			2.01%
Charitable contribution carryforward expiration	(0.18%)
State net operating loss carryforward valuation allowance	(0.59%)
Goodwill impairment	(6.12%)
Remeasurement of deferred income tax liabilities resulting from Tax Cuts and Jobs Act	0.63%
Other	(0.12%)	(1.63%)	(0.79%)
Income tax rate	29.58%	(291.47%)	32.54%