Acquisition (Details)		3 Months Ended		9 Months Ended
	Apr. 01, 2015 USD ($) Loan shares	Sep. 30, 2015 USD ($)	Sep. 30, 2014	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Payments to acquire businesses				$ 45,260,000	$ 0
Number of bank term loan facilities (loan) | Loan	2
Term loan facility		$ 33,750,000		33,750,000		$ 0
Contingent obligation due selling unitholders of Cogent		13,244,000		13,244,000		0
Goodwill		206,182,000		206,182,000		$ 130,976,000
Cogent Partners, LP
Business Acquisition [Line Items]
Payments to acquire businesses	$ 44,000,000
Number of shares issued during acquisition, shares | shares	779,454
Maximum contingent consideration	$ 18,900,000
Conditional consideration, shares | shares	334,048
Number of bank term loan facilities (loan) | Loan	2
Term loan facility	$ 45,000,000.0
Distribution period ending on the second anniversary of the closing (years)	2 years
Distribution period ending on the fourth anniversary of the closing (years)	2 years
Fair value of contingent issuance of common shares at acquisition date	$ 11,900,000
Contingent obligation due selling unitholders of Cogent	13,100,000
Increase in contingent consideration, liability		100,000		100,000
Professional fees		1,200,000
Total purchase price	100,000,000
Goodwill	92,981,000
Amortization expense		200,000		400,000
Escrow deposit	8,900,000
Amount due to sellers are post-closing adjustment		$ 600,000		$ 600,000
Goodwill estimated useful life (years)				15 years
Ratio of compensation to total revenue, percent		54.00%	54.00%	54.00%	54.00%
Cogent 12 Month Facility
Business Acquisition [Line Items]
Term loan facility		$ 11,300,000		$ 11,300,000
Cogent 36 Month Facility
Business Acquisition [Line Items]
Term loan facility		$ 22,500,000		$ 22,500,000
Long-term Debt | Cogent 36 Month Facility | Cogent Partners, LP
Business Acquisition [Line Items]
Term loan facility	22,500,000.0
Short-term Debt | Cogent 12 Month Facility | Cogent Partners, LP
Business Acquisition [Line Items]
Term loan facility	$ 22,500,000.0
Minimum | Cogent Partners, LP
Business Acquisition [Line Items]
Estimated remaining useful life (years)				1 year
Maximum | Cogent Partners, LP
Business Acquisition [Line Items]
Estimated remaining useful life (years)				3 years