Revenue Recognition - Summary of Activity in Each of Product Revenue and Discounts Categories (Detail) $ in Thousands	6 Months Ended
	Sep. 30, 2018 USD ($)
Revenue Recognition And Deferred Revenue [Abstract]
Balance at March 31, 2018	$ 1,405
Provision related to current period revenue	989
Credits and adjustments made during the period	(869)
Balance at September 30, 2018	$ 1,525