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, 2015	Dec. 31, 2014
Deferred income tax assets:
Net operating loss carryforwards	$ 112,193	$ 150,004
Tax credits	40,614	43,804
Compensation	25,752	24,486
Deferred revenue	25,287	13,486
Tax basis in investments	100	5,601
Other	8,246	9,712
Gross deferred income tax assets	212,192	247,093
Less: valuation allowance	(18,742)	(36,174)
Net deferred income tax assets	193,450	210,919
Deferred income tax liabilities:
Depreciation and amortization	(130,645)	(129,825)
Total deferred income tax liabilities	(130,645)	(129,825)
Net deferred income taxes	62,805	81,094
Deferred income taxes / liabilities included in the balance sheet are:
Deferred income tax asset - noncurrent	90,872	94,536
Deferred income tax liability - noncurrent	(28,067)	(13,442)
Net deferred income taxes	$ 62,805	$ 81,094