Bank Loan Facilities - Additional Information (Detail)		12 Months Ended
	Apr. 01, 2015 USD ($) Loan installment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013
Line of Credit Facility [Line Items]
Bank term loans payable		$ 33,750,000	$ 0
Cogent Partners, LP
Line of Credit Facility [Line Items]
Number of bank term loan facilities (loan) | Loan	2
Bank term loans payable	$ 45,000,000
Cogent 12 Month Facility
Line of Credit Facility [Line Items]
Bank term loans payable		$ 11,300,000
Debt term (years)	1 year
Weighted average interest rate (percent)	0.75%	4.31%
Stated minimum interest rate (percent)	4.00%
Cogent 36 Month Facility
Line of Credit Facility [Line Items]
Bank term loans payable		$ 22,500,000
Debt term (years)	3 years
Weighted average interest rate (percent)	1.25%	4.30%
Number of semi-annual installments | installment	4
Amount outstanding to reduce interest rate	$ 7,500,000
Stated minimum interest rate (percent)	4.00%
Cogent 36 Month Facility | Prime Rate
Line of Credit Facility [Line Items]
Spread on interest rate (percent)	0.75%
Long-term Debt | Cogent 36 Month Facility | Cogent Partners, LP
Line of Credit Facility [Line Items]
Bank term loans payable	$ 22,500,000
Short-term Debt | Cogent 12 Month Facility | Cogent Partners, LP
Line of Credit Facility [Line Items]
Bank term loans payable	$ 22,500,000
Line of Credit
Line of Credit Facility [Line Items]
Revolving loan facility, borrowing capacity		$ 50,000,000
Revolving loan facility, maturity date		Apr. 30, 2016
Alternative interest rate (applies if higher than Prime Rate) (percent)		3.25%
Interest rate (applies if higher than alternative interest rate)		U.S. Prime Rate
Weighted average daily borrowings outstanding under the loan facility		$ 35,800,000	$ 33,900,000
Weighted average interest rate (percent)		3.30%	3.30%	3.30%
Line of Credit | Prime Rate
Line of Credit Facility [Line Items]
Spread on interest rate (percent)		3.50%