Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforward, Annual limitation	$ 11,700
Unrealized Built In Gain, For Realizing Future NOLs	$ 176,900
U.S. federal income tax rate	21.00%	35.00%
Change In Valuation Allowance Due To Tax Cuts And Jobs Act	$ 0	$ (64,949)	$ 0
Refundable Alternative Minimum Tax Credits	0	1,402	0
Federal tax net operating loss carryforwards	457,800
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	458,200
Change in valuation allowance	(64,994)	0	$ 0
Deferred income taxes	139,534	$ 0
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Operating Loss Carryforward	(276,100)
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Operating Loss Carryforward	(14,000)
Increase (Decrease) in Tax Credit Carryforward	(8,200)
Fifth Creek [Member]
Operating Loss Carryforwards [Line Items]
Deferred income taxes	$ 137,700