Intangible Assets - Reconciliation of Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Gross carrying cost at beginning of period			$ 68,322	$ 36,349
Acquisition of Icon Bioscience Inc.			0	31,973
Gross carrying cost at end of period	$ 68,322	$ 68,322	68,322	68,322
Accumulated amortization at beginning of period			(38,193)	(36,349)
Amortization expense	(615)	(615)	(1,230)	(615)
Accumulated amortization at end of period	(39,423)	(36,964)	(39,423)	(36,964)
Net book value at end of period	$ 28,899	$ 31,358	$ 28,899	$ 31,358	$ 30,129