Income Taxes - Summary of NOLs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Operating Loss (Taxable)	$ (7,610,808)
Limitations	(1,589,798)
Net Operating Loss (Taxable)	$ (6,021,010)
December 31, 2011 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2011
Operating Loss (Taxable)	$ (14,201)
Net Operating Loss (Taxable)	$ (14,201)
Expiration (if unused) Year Ended	Dec. 31, 2031
December 31, 2012 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2012
Operating Loss (Taxable)	$ (7,535,083)
Limitations	(1,589,798)
Net Operating Loss (Taxable)	$ (5,945,285)
Expiration (if unused) Year Ended	Dec. 31, 2032
December 31, 2013 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2013
Operating Loss (Taxable)	$ (5,019)
Net Operating Loss (Taxable)	$ (5,019)
Expiration (if unused) Year Ended	Dec. 31, 2033
December 31, 2014 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2014
Operating Loss (Taxable)	$ (32,389)
Net Operating Loss (Taxable)	$ (32,389)
Expiration (if unused) Year Ended	Dec. 31, 2034
December 31, 2015 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2015
Operating Loss (Taxable)	$ (12,347)
Net Operating Loss (Taxable)	$ (12,347)
Expiration (if unused) Year Ended	Dec. 31, 2035
December 31, 2016 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2016
Operating Loss (Taxable)	$ (4,617)
Net Operating Loss (Taxable)	$ (4,617)
Expiration (if unused) Year Ended	Dec. 31, 2036
December 31, 2017 [Member]
Operating Loss Carryforwards [Line Items]
Originated During Year Ended	Dec. 31, 2017
Operating Loss (Taxable)	$ (7,152)
Net Operating Loss (Taxable)	$ (7,152)
Expiration (if unused) Year Ended	Dec. 31, 2037