Notes Payable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument
Notes payable	$ 202,700	$ 208,809
Senior Notes due April 2025
Debt Instrument
Notes payable	148,493	148,455
Unamortized discount	1,507	1,545
FHLB notes
Debt Instrument
Notes payable	6,857	19,402
Unamortized premium	281	436
NLIC note payable due May 2033
Debt Instrument
Notes payable	10,000	10,000
NLIC note payable due September 2033
Debt Instrument
Notes payable	10,000	10,000
ASIC note payable due April 2034
Debt Instrument
Notes payable	7,500	7,500
Insurance company line of credit due December 31, 2018
Debt Instrument
Notes payable	1,000	1,000
Ventures Management line of credit
Debt Instrument
Notes payable	$ 18,850	$ 12,452