Changes in Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	$ 244,641	$ 210,360
Other comprehensive (loss) income before reclassifications	387	(666)
Ending Balance, Amount	649,958	244,641
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(397)	379
Other comprehensive (loss) income before reclassifications	(213)	(776)
Ending Balance, Amount	(610)	(397)
Unrealized Gain (Loss) on Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(326)	(436)
Other comprehensive (loss) income before reclassifications	600	110
Ending Balance, Amount	274	(326)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance, Amount	(723)	(57)
Ending Balance, Amount	$ (336)	$ (723)