Bank Loan Facilities - Additional Information (Details)					1 Months Ended		6 Months Ended
	Apr. 30, 2018 USD ($)	Oct. 31, 2017 USD ($)	Aug. 04, 2017 USD ($)	Apr. 30, 2015 USD ($) Loan installment	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Aug. 08, 2017 USD ($)	Aug. 07, 2017 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Term loan facility							$ 11,250,000					$ 16,875,000
Repayment of bank term loans							$ 5,625,000	$ 11,250,000
Cogent 12 Month Facility
Line of Credit Facility [Line Items]
Interest rate, percent				4.00%
Weighted average interest rate (percent)							5.12%	4.75%
Cogent 36 Month Facility
Line of Credit Facility [Line Items]
Interest rate, percent				4.00%
Weighted average interest rate (percent)				1.25%			5.12%	4.75%
Term loan facility							$ 11,300,000
Debt instrument term (years)				3 years
Number of semi-annual installments (installment) | installment				4
Debt instrument, amount outstanding to reduce interest rate				$ 7,500,000
Repayment of bank term loans					$ 5,600,000
Cogent 36 Month Facility | Scenario, Forecast
Line of Credit Facility [Line Items]
Repayment of bank term loans	$ 5,600,000	$ 5,600,000
Cogent 36 Month Facility | Subsequent Event
Line of Credit Facility [Line Items]
Debt instrument term (years)			3 years
Basis spread on variable rate (percent)			0.75%
Repayment of bank term loans			$ 5,600,000
Cogent 36 Month Facility | Prime Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)				0.75%
Cogent Partners, LP
Line of Credit Facility [Line Items]
Term loan facility				$ 45,000,000
Number of bank term loan facilities (loan) | Loan				2
Cogent Partners, LP | Cogent 12 Month Facility | Short-term Debt
Line of Credit Facility [Line Items]
Term loan facility				$ 22,500,000
Cogent Partners, LP | Cogent 36 Month Facility | Long-term Debt
Line of Credit Facility [Line Items]
Term loan facility				$ 22,500,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving loan facility, maximum borrowing capacity							$ 80,000,000				$ 70,000,000
Increase in maximum borrowing capacity						$ 10,000,000
Interest rate, percent							3.50%
Weighted average daily borrowings outstanding under the loan facility							$ 62,700,000	$ 49,300,000
Weighted average interest rate (percent)							3.89%	3.50%
Revolving Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Revolving loan facility, maximum borrowing capacity									$ 90,000,000.0	$ 80,000,000.0
Revolving Credit Facility | Prime Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)							4.25%