Income Taxes - Deferred Tax Assets and Liabilities Result from Differences in Timing of Recognition of Certain Income and Expense Items for Tax and Financial Accounting Purposes (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax assets:
Net operating loss carryforwards	$ 65,351	$ 112,193
Tax credits	25,173	40,614
Compensation	39,340	25,752
Deferred revenue	27,303	25,287
Other	6,279	8,346
Gross deferred income tax assets	163,446	212,192
Less: valuation allowance	(9,659)	(18,742)
Net deferred income tax assets	153,787	193,450
Deferred income tax liabilities:
Depreciation and amortization	(102,657)	(130,645)
Total deferred income tax liabilities	(102,657)	(130,645)
Net deferred income taxes	51,130	62,805
Deferred income taxes / liabilities included in the balance sheet are:
Deferred income tax asset-noncurrent	77,479	90,872
Deferred income tax liability-noncurrent	(26,349)	(28,067)
Net deferred income taxes	$ 51,130	$ 62,805