Summary of Significant Accounting Policies - Schedule of Impact on Consolidated Statement of Cash Flows on Adoption of Topic 606 (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash Flows from Operating Activities:
Net income	$ 114,833	$ (36,466)
Imputed interest income from licensing	(8,253)
Changes in accounts receivable	8,879	982
Changes in prepaid expenses	1,644	(657)
Changes in other current assets	(585)	(242)
Changes in accrued expenses and other current liabilities	2,566	$ (31)
Changes in deferred revenue	600
Changes in other liabilities	(99)
Cumulative Adjustment for Adoption of Topic 606 [Member] | ASU 2014-09 [Member]
Cash Flows from Operating Activities:
Net income	(1,111)
Imputed interest income from licensing	(8,253)
Changes in accounts receivable	8,578
Changes in prepaid expenses	(60)
Changes in other current assets	350
Changes in accrued expenses and other current liabilities	(5)
Changes in deferred revenue	600
Changes in other liabilities	(99)
Results Without Adoption of Topic 606 | ASU 2014-09 [Member]
Cash Flows from Operating Activities:
Net income	115,944
Changes in accounts receivable	301
Changes in prepaid expenses	1,704
Changes in other current assets	(935)
Changes in accrued expenses and other current liabilities	$ 2,571