Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Provision for income taxes (benefit) expense related to remeasurement of net deferred tax liability	$ (28,400)		$ (28,400)
U.S. statutory federal income tax rate			35.00%	35.00%	35.00%
Net long-term deferred tax asset	2,900		$ 2,900	$ 2,400
Net long-term deferred tax liability	51,619		51,619	76,447
Gross deferred tax assets related to state net operating loss carryforwards	282,000		282,000
Valuation allowance related to certain state net operating loss carryforward deferred tax assets	8,000		8,000
Liabilities recorded related to unrecognized tax benefits				5,200
Liabilities related to interest and penalties	600		600	800
Unrecognized tax benefit that would affect income tax rate if recognized	$ 4,700		$ 4,700	$ 3,300
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss expiration date			Net operating loss carryforwards that will expire between 2018 and 2037
Operating loss expiration, beginning year			2018
Operating loss expiration, ending year			2037
State and Local Jurisdiction [Member] | Tax Year 2017 [Member]
Income Taxes [Line Items]
Income tax examination year			2017
State and Local Jurisdiction [Member] | Tax Year 2013 [Member]
Income Taxes [Line Items]
Income tax examination year			2013
U.S. Federal Income Tax Authority [Member] | Internal Revenue Service [Member] | Tax Year 2014 [Member]
Income Taxes [Line Items]
Income tax examination year			2014
U.S. Federal Income Tax Authority [Member] | Internal Revenue Service [Member] | Tax Year 2017 [Member]
Income Taxes [Line Items]
Income tax examination year			2017
Scenario, Forecast [Member]
Income Taxes [Line Items]
U.S. statutory federal income tax rate		21.00%