Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	May 31, 2016	Mar. 31, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Contingencies And Commitments [Line Items]
Lease termination date			May 31, 2018
Monthly base rent charges		$ 100,000
Annual increase lease payment		1.40%
Standby letter of credit		$ 300,000
Rent expense			$ 1,700,000	$ 1,600,000	$ 1,700,000
Issuance of stock under consulting agreement, value			$ 767,000	$ 359,000
Common Stock [Member]
Contingencies And Commitments [Line Items]
Issuance of stock under consulting agreement, shares			188,462	27,221
Letter Agreement with Dr. Stelios Papadopoulos [Member]
Contingencies And Commitments [Line Items]
Letter agreement effective date			Jul. 01, 2016
Letter agreement term	36 months
Quarterly retainer payable	$ 200,000
Aggregate retainer fee payable	$ 2,500,000		$ 1,260,000
Percentage of M&A transaction fee payable	1.00%
Issuance of stock under consulting agreement, value			$ 800,000	$ 400,000
Letter Agreement with Dr. Stelios Papadopoulos [Member] | Common Stock [Member]
Contingencies And Commitments [Line Items]
Issuance of stock under consulting agreement, shares			188,462	27,221
Maximum [Member]
Contingencies And Commitments [Line Items]
Non-rent shared tenant occupancy costs		$ 200,000