Senior Notes, Convertible Notes and Trust Preferred Securities - Schedule of Maturities of Long-term Debt (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (7,258)
Senior Notes, Convertible Notes, and Trust Preferred Securities [Member]
Debt Instrument [Line Items]
2018	0
2019	0
2020	0
2021	0
2022	0
Thereafter	629,120
Long-term debt, gross	629,120
Unamortized debt discounts	(1,507)
Unamortized debt issuance costs	(5,219)
Long-term debt	$ 622,394

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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