Related Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Recognized revenue	$ 4,149,000	$ 243,000	$ 4,149,000	$ 520,000
Accounts receivable	4,149,000		4,149,000
Roche [Member]
Related Party Transaction [Line Items]
Recognized revenue	$ 4,149,000	$ 243,000	$ 4,149,000	$ 520,000
Related party revenue to net revenue, percentage	18.50%	1.70%	9.90%	2.00%
Accounts receivable	$ 4,149,000		$ 4,149,000		$ 0
Amount of related party transaction during the period	0	$ 0	0	$ 0
Board of Directors [Member]
Related Party Transaction [Line Items]
Recognized revenue	484,000	$ 98,500	1,312,000	$ 130,500
Accounts receivable	$ 1,294,000		$ 1,294,000		$ 419,000