Senior Notes, Convertible Notes and Trust Preferred Securities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2007	May 31, 2014	Jun. 30, 2013	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt satisfaction (gains) charges, net	$ 975,000	$ (25,150,000)	$ 9,452,000
Debt issuance costs, net	7,126,000
Convertible Debt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt interest rate percentage							6.00%
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%
Long-term debt	0
Original debt, amount	$ 12,400,000	$ 3,828,000	$ 12,763,000
Shares issued (in shares)	1,892,269	519,664	1,904,542
Cash payments	$ 672,000	$ 529,000	$ 233,000
Debt satisfaction (gains) charges, net	436,000	476,000	$ 2,436,000
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%
Principal amount outstanding on Trust Preferred Securities	129,120,000
Debt issuance costs, net	2,024,000	2,124,000
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%
Senior Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Face amount	500,000,000	500,000,000
Long-term debt	494,362,000	493,526,000
Debt issuance costs, net	3,858,000	4,421,000
Senior Notes [Member] | Senior Notes Due 2024 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Face amount	$ 250,000,000	$ 250,000,000
Debt interest rate percentage	4.40%	4.40%			4.40%
Senior Notes [Member] | Senior Notes Due 2023 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Face amount	$ 250,000,000	$ 250,000,000
Debt interest rate percentage	4.25%	4.25%				4.25%