Significant Customers and Concentrations of Risk - Summary of Significant Customers from which the Company Derived 10% or More of Total Revenue (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Total revenues		$ 14,040	$ 15,052	$ 13,416	$ 12,007	$ 14,196	$ 13,479	$ 12,228	$ 12,319	$ 54,515	$ 52,222	$ 45,658
Teva [Member]
Concentration Risk [Line Items]
Total revenues										20,949	24,941	17,715
AMAG [Member]
Concentration Risk [Line Items]
Total revenues										8,965	4,446	365
McKesson [Member]
Concentration Risk [Line Items]
Total revenues	[1]									8,707	7,600	6,837
AmerisourceBergen [Member]
Concentration Risk [Line Items]
Total revenues	[1]									6,098	4,903	4,527
Ferring [Member]
Concentration Risk [Line Items]
Total revenues										$ 5,258	$ 6,283	6,117
LEO Pharma [Member]
Concentration Risk [Line Items]
Total revenues												$ 6,000

[1] Revenue net of estimated sales returns and allowances based on OTREXUP® shipments to the distributor.