Acquisition (Details) $ in Thousands		12 Months Ended
	Apr. 01, 2015 USD ($) Loan shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2015 USD ($)
Business Acquisition [Line Items]
Payments to acquire Cogent Partners, LP		$ 45,265	$ 0	$ 0
Bank term loans payable		33,750	0
Contingent obligation due selling unitholders of Cogent		13,647	0
Losses on fair value of contingent obligation		503	0	0
Goodwill		209,024	$ 130,976	$ 142,972
Cogent 12 Month Facility
Business Acquisition [Line Items]
Bank term loans payable		11,300
Cogent 36 Month Facility
Business Acquisition [Line Items]
Bank term loans payable		22,500
Cogent Partners, LP
Business Acquisition [Line Items]
Ownership percent acquired	100.00%
Payments to acquire Cogent Partners, LP	$ 44,000
Common stock paid at acquisition closing (shares) | shares	779,454
Contingent consideration, cash	$ 18,900
Possible contingent consideration (shares) | shares	334,048
Number of bank term loan facilities (loan) | Loan	2
Bank term loans payable	$ 45,000
Fair value of contingent common shares	11,900
Contingent obligation due selling unitholders of Cogent	13,100
Losses on fair value of contingent obligation		500
Transaction costs		1,200
Purchase price	100,000
Goodwill	93,116
Amortization expense		500
Escrow deposit	8,900
Amount to trigger post-closing distribution payment					$ 5,000
Post closing distribution		$ 7,900
Goodwill useful life (years)		15 years
Ratio of compensation to total revenue (percent)		54.00%	54.00%
Cogent Partners, LP | Minimum
Business Acquisition [Line Items]
Intangible assets useful life (years)		1 year
Cogent Partners, LP | Maximum
Business Acquisition [Line Items]
Intangible assets useful life (years)		3 years
Cogent Partners, LP | Long-term Debt | Cogent 36 Month Facility
Business Acquisition [Line Items]
Bank term loans payable	22,500
Cogent Partners, LP | Short-term Debt | Cogent 12 Month Facility
Business Acquisition [Line Items]
Bank term loans payable	$ 22,500