Schedule II - Condensed Financial Information of Registrant, Parenthetical (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Balance Sheets [Abstract]
Equity securities available-for-sale, cost		$ 144,274
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	21,615,105	21,455,545
Common stock, shares outstanding (in shares)	21,615,105	21,455,545
Condensed Statements of Income [Abstract]
Operating expense, affiliated	$ 2,129	$ 1,825	$ 1,860
Condensed Statements of Cash Flows [Abstract]
Dividends paid to stockholders, affiliated	(10,477)	(10,006)	(9,182)
Parent company [Member]
Condensed Balance Sheets [Abstract]
Equity securities available-for-sale, cost	$ 0	$ 2,000
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	21,615,105	21,455,545
Common stock, shares outstanding (in shares)	21,615,105	21,455,545
Condensed Statements of Income [Abstract]
Operating expense, affiliated	$ 1,243	$ 1,124	1,139
Condensed Statements of Cash Flows [Abstract]
Dividends paid to stockholders, affiliated	$ (10,477)	$ (10,006)	$ (9,182)