Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 31, 2013	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Commitments [Line Items]
Operating leases, expiration year				2021
Rent expense		$ 220,000	$ 273,000	$ 484,000	$ 533,000
Bellevue [Member] | Washington [Member]
Other Commitments [Line Items]
Expiration date of operating lease	2014-08
Extended expiration date of operating lease	2020-05