Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fair value of bonds held-to-maturity	$ 8,968,690	$ 8,130,084
Amortized cost of bonds available-for-sale	6,435,670	6,261,621
Cost of equity securities	663,058	714,504
Accumulated depreciation of investment real estate	256,757	267,920
Property and equipment, net of accumulated depreciation	$ 257,907	$ 236,922
Common stock, par value (in usd per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	30,832,449	30,832,449
Common stock, shares outstanding (in shares)	26,887,200	26,885,449