Fixed Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 68,851	$ 66,275
Less: Accumulated depreciation and amortization		(28,355)	(23,867)
Fixed assets, net		40,496	42,408
Other Depreciation and Amortization		7,000	7,700	$ 6,800
Gain (Loss) on Disposition of Property Plant Equipment		2,346	0	(54)
Telephone and computer equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		3,465	2,787
Computer software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		2,914	2,167
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		1,423	1,204
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		36,702	35,092
Assets acquired under capital leases-equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		6,920	4,075
Depreciation		1,000	1,200	$ 1,500
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		3,400	2,400
Aircraft and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		17,369	20,893
Less: Accumulated depreciation and amortization		(1,800)	(1,700)
Gain (Loss) on Disposition of Property Plant Equipment	$ 2,300
Depreciation		1,500	1,700
Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 58	$ 57