Senior Notes, Convertible Notes and Trust Preferred Securities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2007	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt satisfaction (gains) charges, net	$ 2,596,000	$ (6,196,000)	$ 975,000
Convertible Debt [Member] | Six Percent Convertible Guaranteed Note [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Face amount					$ 115,000,000
Debt interest rate percentage					6.00%
Original debt, amount			$ 12,400,000
Shares issued (in shares)			1,892,269
Cash payments			$ 672,000
Debt satisfaction (gains) charges, net			$ 436,000
6.804% Trust Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Face amount				$ 200,000,000
Debt interest rate percentage				6.804%
Effective interest percentage	4.22%
Principal amount outstanding on Trust Preferred Securities	$ 129,120,000	129,120,000
Debt issuance costs, gross	$ 1,824,000	$ 1,924,000
6.804% Trust Preferred Securities [Member] | London Interbank Offered Rate (LIBOR) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Basis spread on variable rate				1.70%