Commitments and Contingencies - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2016
Business Acquisitions [Member]
Other Commitments [Line Items]
Number of contingent additional shares earned including dividend equivalent amount	437,416
Business Acquisitions [Member] | Class A Common Stock [Member]
Other Commitments [Line Items]
Common stock issued and issuable		40,585
Business Acquisitions [Member] | Class A Common Stock [Member] | Non-Contingent [Member]
Other Commitments [Line Items]
Common stock issued and issuable		202,984
Business Acquisitions [Member] | Class A Common Stock [Member] | Maximum [Member]
Other Commitments [Line Items]
Contingent shares issuable upon satisfaction of performance thresholds		447,443
LFB [Member]
Other Commitments [Line Items]
Guarantees indemnifications	$ 2,422,000
Collateral/counter-guarantees	2,422,000
Other commitments	0
LFNY [Member]
Other Commitments [Line Items]
Other commitments	$ 0