Fair Value Measurements - Fair Value Measurement Activity for Liabilities Utilize Level 3 Inputs (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning	$ 18,658	$ 14,445
Ending	18,946	18,658
Deferred development costs [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	(195)	(744)
Talon CVR [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	$ 483	$ 4,957