Convertible Debt and Notes Payable (Details)		12 Months Ended
		Dec. 31, 2019 USD ($) letters_of_credit $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Jul. 01, 2019 USD ($)	May 07, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 11, 2018 USD ($)	Dec. 14, 2017 USD ($) $ / shares	Dec. 08, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 10, 2014 USD ($)
Debt and Capital Lease Obligations [Line Items]
Finance Lease, Right-of-Use Asset, Amortization		$ 1,266,000	$ 1,627,000
Finance Lease, Interest Expense		227,000	231,000
Finance Lease, Interest Payment on Liability		227,000	231,000
Finance Lease, Principal Payments		1,266,000	2,186,000
Components of short-term borrowings and other debt
Convertible debt	[1]	118,688,000	134,489,000
Note payable		306,818,000	229,740,000
Loans Payable to Bank		32,180,000	28,200,000
Other Notes Payable		2,516,000	0
Capital lease obligations		3,937,000	5,025,000
Debt, Long-term and Short-term, Combined Amount		464,139,000	397,454,000
Purchase of treasury stock, cost		34,500,000
Amortization of debt discount		4,598,000	5,473,000	$ 7,435,000
Debt Instrument, Periodic Payment, Principal		100,000
Letter of credit, borrowing capacity		395,000,000
Future minimum lease payments for capital lease obligations
2020		1,290,000
2021		1,398,000
2022		1,166,000
2023		411,000
2024		11,000
Thereafter		0
Subtotal		4,276,000
Less: Amount representing interest	[2]	(339,000)
Capital lease obligations		$ 3,937,000	5,025,000
Number of letters of credit | letters_of_credit		6
Cash collateral pledged		$ 6,563,000	$ 6,318,000	17,888,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01
Finance Lease, Weighted Average Remaining Lease Term		3 years 2 months 15 days
Finance Lease, Weighted Average Discount Rate, Percent		4.88%
Other Long-term Debt		$ 2,500,000
Borrowings on other long term debt		2,600,000
Letter of Credit, Boston Office, Expires March 2020 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		382,000
Letter of Credit, NY Office 1, Expires April 2020 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		359,000
Letter of Credit, NY Office 3, Expires October 2020 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		398,000
Letter of Credit, NY Office 4, Expires October 2020 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		1,125,000
Letter of Credit, NY Office 5, Expires November 2020 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		1,629,000
Letter of Credit, San Francisco Office, Expires October 2025 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		716,000
Convertible Debt
Components of short-term borrowings and other debt
Convertible debt, unamortized discount		14,900,000	$ 19,500,000
Repayments on long-term and short-term borrowings
2020		4,050,000
2021		4,050,000
2022		139,050,000
2023		0
2024		0
Thereafter		0
Subtotal		147,150,000
Less: Amount representing interest	[2]	(28,462,000)
Senior Notes
Components of short-term borrowings and other debt
Note payable		306,818,000
Repayments on long-term and short-term borrowings
2020		23,548,000
2021		23,548,000
2022		23,548,000
2023		23,548,000
2024		98,721,000
Thereafter		334,304,000
Subtotal		527,217,000
Less: Amount representing interest	[2]	(220,399,000)
Loans
Repayments on long-term and short-term borrowings
2020		33,126,000
2021		0
2022		0
2023		0
2024		0
Thereafter		0
Subtotal		33,126,000
Less: Amount representing interest	[2]	(946,000)
Insurance Note and Aircraft
Repayments on long-term and short-term borrowings
2020		593,000
2021		593,000
2022		593,000
2023		593,000
2024		543,000
Thereafter		0
Subtotal		2,915,000
Less: Amount representing interest	[2]	$ (399,000)
Insurance Note
Components of short-term borrowings and other debt
Interest rate		2.51%
Interest Expense, Debt, Excluding Amortization		$ 100,000
Debt Instrument, Periodic Payment, Principal		200,000
Notes Payable to Banks
Components of short-term borrowings and other debt
Debt Instrument, Face Amount					$ 4,000,000.0						$ 28,200,000
Interest Expense, Debt, Excluding Amortization		$ 1,800,000	1,600,000	700,000
Short-term Debt, Percentage Bearing Variable Interest Rate		3.75%
2022 convertible note | Convertible Debt
Components of short-term borrowings and other debt
Convertible debt		$ 135,000,000.0
Debt Instrument, Face Amount									$ 135,000,000.0
Debt Instrument, Convertible, Conversion Price | $ / shares									$ 17.375
Purchase of treasury stock, cost		19,500,000
Interest on Convertible Debt, Net of Tax		4,100,000	4,100,000	200,000
Convertible debt, unamortized discount									$ 23,400,000			$ 23,400,000
Amortization of debt discount		4,300,000	4,000,000.0	200,000
Debt Instrument, Interest Rate, Effective Percentage									7.13%
Debt Issuance Costs, Gross									$ 2,200,000
2019 convertible note | Convertible Debt
Components of short-term borrowings and other debt
Debt Instrument, Face Amount												$ 149,500,000
Debt Instrument, Repurchase Amount									115,100,000
Interest on Convertible Debt, Net of Tax		100,000	1,100,000	4,300,000
Amortization of debt discount		300,000	1,500,000	7,300,000
Debt Instrument, Interest Rate, Effective Percentage												8.89%
Interest rate												3.00%
2024 Notes | Senior Notes
Components of short-term borrowings and other debt
Debt Instrument, Face Amount						$ 53,000,000.0
Debt Issuance Costs, Gross		600,000				$ 1,500,000
Interest rate						7.25%
Debt Instrument, Additional amount issued		25,000,000.0
Debt Instrument, Unamortized Premium		500,000
Interest Expense, Debt, Excluding Amortization		2,900,000
2033 Notes | Senior Notes
Components of short-term borrowings and other debt
Debt Instrument, Face Amount							$ 10,000,000.0	$ 90,000,000.0
Debt Issuance Costs, Gross								$ 3,600,000
Interest rate								7.75%
Interest Expense, Debt, Excluding Amortization		7,700,000	4,300,000
2027 Notes | Senior Notes
Components of short-term borrowings and other debt
Debt Instrument, Face Amount									$ 18,000,000.0	$ 120,000,000.0
Debt Issuance Costs, Gross										$ 5,000,000.0
Interest rate										7.35%
Interest Expense, Debt, Excluding Amortization		10,100,000	10,100,000	$ 600,000
Insurance Note
Components of short-term borrowings and other debt
Short-term Debt, Maximum Amount Outstanding During Period		2,200,000
Revolving Credit Facility
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		95,000,000
Revolving Credit Facility | BMO Harris Bank
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity		25,000,000
Collateral Reinsurance Agreement
Future minimum lease payments for capital lease obligations
Cash collateral pledged		$ 2,000,000.0	$ 1,000,000.0

[1] The carrying amount of the convertible debt includes an unamortized discount of $14.9 million and $19.5 million as of December 31, 2019 and 2018, respectively.

[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.