Income Taxes - Summary of Changes in Deferred Tax Assets Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning Balance	$ 69,593	$ 89,251	$ 1,044,152
Credited to provision (benefit) for income taxes	(23,670)	(15,981)	(954,487)
Charged (credited) to other comprehensive income and other	15,533	(3,677)	(414)
Ending Balance	$ 61,456	$ 69,593	$ 89,251