Convertible Debt and Notes Payable (Details)			3 Months Ended		9 Months Ended		40 Months Ended
		Dec. 05, 2016	Sep. 30, 2017 USD ($) letters_of_credit	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) letters_of_credit	Sep. 30, 2016 USD ($)	Jan. 31, 2014 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2016	Oct. 10, 2014 USD ($)	Mar. 10, 2014 USD ($) $ / shares
Debt and Capital Lease Obligations [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio		0.25
Components of short-term borrowings and other debt
Convertible debt	[1]		$ 136,189,000		$ 136,189,000			$ 130,029,000
Note payable			61,141,000		61,141,000			60,953,000
Loans Payable to Bank			28,082,000		28,082,000			0
Other Notes Payable			8,895,000		8,895,000			14,237,000
Capital lease obligations			3,149,000		3,149,000			1,840,000
Debt, Long-term and Short-term, Combined Amount			237,456,000		237,456,000			207,059,000
Amortization of debt discount					5,601,000	$ 5,107,000
Letter of credit, borrowing capacity			305,000,000		305,000,000
Capital Lease Obligations Incurred							$ 5,500,000
Capital Leases, Income Statement, Interest Expense			100,000	$ 100,000	100,000	100,000
Future minimum lease payments for capital lease obligations
2017			467,000		467,000
2018			1,699,000		1,699,000
2019			399,000		399,000
2020			320,000		320,000
2021			320,000		320,000
Thereafter			160,000		160,000
Subtotal			3,365,000		3,365,000
Less: Amount representing interest	[2]		(216,000)		(216,000)
Capital lease obligations			$ 3,149,000		$ 3,149,000			1,840,000
Number of Letters of Credit | letters_of_credit			8		8
Minimum
Components of short-term borrowings and other debt
Capital Lease Obligation, Initial Term					48 months
Capital leases, interest rate			4.25%		4.25%
Maximum
Components of short-term borrowings and other debt
Capital Lease Obligation, Initial Term					60 months
Capital leases, interest rate			5.69%		5.69%
Cash Convertible Note Economic Hedge And Warrant Transaction
Components of short-term borrowings and other debt
Cash convertible note hedge transaction						20,500,000
Treasury Stock
Components of short-term borrowings and other debt
Cash convertible note hedge transaction						300,000
Letter of Credit, San Francisco Office, Expires January 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			$ 710,157		$ 710,157
Letter of Credit, Connecticut Office, Expires January 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			65,000		65,000
Letter of Credit, Boston Office, Expires March 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			381,700		381,700
Letter of Credit, NY Office 1, Expires April 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			354,939		354,939
Letter of Credit, NY Office 2, Expires May 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			69,750		69,750
Letter of Credit, NY Office 3, Expires October 2017 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			595,540		595,540
Letter of Credit, NY Office 4, Expires October 2017 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			2,811,204		2,811,204
Letter of Credit, NY Office 5, Expires November 2017 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			1,600,000		1,600,000
Convertible Debt
Components of short-term borrowings and other debt
Interest rate											3.00%
Principal amount of notes being converted											$ 1,000
Interest on Convertible Debt, Net of Tax			1,100,000	1,100,000	3,400,000	3,400,000
Debt Instrument, Convertible, Conversion Price | $ / shares											$ 21.32
Convertible debt, unamortized discount			12,200,000		12,200,000			$ 17,800,000			$ 35,700,000
Amortization of debt discount			1,900,000	1,700,000	5,600,000	5,100,000
Debt Instrument, Interest Rate, Effective Percentage											8.89%
Debt Issuance Costs, Gross											$ 3,700,000
Debt Instrument, Face Amount											$ 149,500,000.0
Repayments on long-term and short-term borrowings
2017			0		0
2018			4,485,000		4,485,000
2019			151,743,000		151,743,000
2020			0		0
2021			0		0
Thereafter			0		0
Subtotal			156,228,000		156,228,000
Less: Amount representing interest	[2]		(20,039,000)		(20,039,000)
Senior Notes
Components of short-term borrowings and other debt
Note payable			61,141,000		61,141,000
Interest rate										8.25%
Interest on Convertible Debt, Net of Tax			1,300,000	1,300,000	3,900,000	3,900,000
Debt Issuance Costs, Gross										$ 2,900,000
Debt Instrument, Face Amount										$ 63,250,000.000
Repayments on long-term and short-term borrowings
2017			1,305,000		1,305,000
2018			5,218,000		5,218,000
2019			5,218,000		5,218,000
2020			5,218,000		5,218,000
2021			68,468,000		68,468,000
Thereafter			0		0
Subtotal			85,427,000		85,427,000
Less: Amount representing interest	[2]		$ (24,286,000)		$ (24,286,000)
Notes Payable to Banks [Member]
Components of short-term borrowings and other debt
Short-term Debt, Percentage Bearing Variable Interest Rate			3.75%		3.75%
Debt Instrument, Face Amount			$ 28,200,000.0		$ 28,200,000.0
Interest Expense, Debt			400,000		400,000
Insurance Note [Member]
Components of short-term borrowings and other debt
Other Notes Payable			400,000		400,000
Interest rate									1.50%
Debt Instrument, Periodic Payment, Principal					200,000
Short-term Debt, Maximum Amount Outstanding During Period					2,100,000
Loans
Repayments on long-term and short-term borrowings
2017			0		0
2018			29,260,000		29,260,000
2019			0		0
2020			0		0
2021			0		0
Thereafter			0		0
Subtotal			29,260,000		29,260,000
Less: Amount representing interest	[2]		(1,178,000)		(1,178,000)
Insurance Note and Aircraft [Member]
Repayments on long-term and short-term borrowings
2017			862,000		862,000
2018			1,933,000		1,933,000
2019			3,410,000		3,410,000
2020			1,363,000		1,363,000
2021			2,512,000		2,512,000
Thereafter			0		0
Subtotal			10,080,000		10,080,000
Less: Amount representing interest	[2]		(1,185,000)		(1,185,000)
Aircraft and related equipment
Components of short-term borrowings and other debt
Other Notes Payable			8,500,000		8,500,000
Interest Expense, Debt			200,000	$ 200,000	$ 600,000	$ 500,000
Aircraft and related equipment | Minimum
Components of short-term borrowings and other debt
Interest rate									4.21%
Aircraft and related equipment | Maximum
Components of short-term borrowings and other debt
Interest rate									7.25%
Common Stock Class A
Components of short-term borrowings and other debt
Class of Warrant, Exercise Price of Warrants or Rights | $ / shares											$ 28.72
Convergex Group [Member]
Components of short-term borrowings and other debt
Capital Lease Obligations Incurred			$ 800,000

[1] The carrying amount of the convertible debt includes an unamortized discount of $12.2 million and $17.8 million as of September 30, 2017 and December 31, 2016.

[2] Amount necessary to reduce net minimum payments to present value calculated at the Company's implicit rate at inception. This amount also includes capitalized debt costs and the unamortized discount on the convertible debt.