Summary of Significant Accounting Policies - Summary of Revenue from Contracts with Customers by Payor Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	$ 7,753	$ 5,370
Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Type of Revenue [Extensible List]	flgt:GeneticTestingServicesMember	flgt:GeneticTestingServicesMember
Revenue from contracts with customers by payor type	$ 7,753	$ 5,370
Clinical Institutional Contracts | Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	7,478	5,119
Clinical Patient Contracts | Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	141	102
Clinical Insurance Contracts | Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	$ 134	$ 149