Schedule II - Condensed Financial Information of Registrant, Parenthetical (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheets [Abstract]
Equity securities available-for-sale, cost	$ 147,479	$ 144,176
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)	21,222,535	20,780,439
Common stock, shares outstanding (in shares)	21,222,535	20,780,439
Condensed Statements of Income [Abstract]
Operating expense, affiliated	$ 1,860	$ 1,822	$ 1,570
Condensed Statements of Cash Flows [Abstract]
Dividends paid to stockholders, affiliated	(9,182)	(8,162)	(7,377)
Parent company [Member]
Condensed Balance Sheets [Abstract]
Equity securities available-for-sale, cost	$ 2,000	$ 0
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)	21,222,535	20,780,439
Common stock, shares outstanding (in shares)	21,222,535	20,780,439
Condensed Statements of Income [Abstract]
Operating expense, affiliated	$ 1,139	$ 1,074	777
Condensed Statements of Cash Flows [Abstract]
Dividends paid to stockholders, affiliated	$ (9,182)	$ (8,162)	$ (7,377)