Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale amortized cost	$ 9,852,710	$ 9,950,773
Equity securities, cost	3,021,179	2,971,856
Senior long-term debt and other debt, estimated fair value	$ 3,113,000	$ 3,030,000