Income Taxes Changes in Balance of Deferred Tax Asset Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Asset Valuation Allowance [Roll Forward]
Beginning Balance	$ (458,288)	$ (69,900)	$ (84,137)
Additions	(766,012)	(408,252)	(20,568)
Deductions	10,550	19,864	34,805
Ending Balance	$ (1,213,750)	$ (458,288)	$ (69,900)