Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 9,669,656	$ 9,591,734
Equity securities, cost	2,653,010	2,481,448
Senior long-term debt and other debt, estimated fair value	$ 2,712,000	$ 2,721,000