Derivative Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount	$ 41,196,629	$ 33,372,000
Cash flow hedges [Member] | Interest rate contracts [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount	$ 0	$ 0	$ 3,724,000
Minimum [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative foreign currency exchange contracts durations	1 month
Maximum [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative foreign currency exchange contracts durations	3 months