Schedule II Condensed Financial Information of Registrant (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows - operating activities
Interest expense paid	$ (11,754)	$ (13,521)	$ (13,902)
Federal income taxes recovered	27,847	24,861	29,195
Other, net, including settlement of payables to subsidiaries	(20,312)	(6,101)	(17,437)
Net cash provided by operating activities	207,418	207,043	221,933
Cash flows - investing activities
Net cash provided by (used in) investing activities	(325,360)	(415,849)	(565,515)
Cash flows - financing activities
Dividends paid to shareholders	(44,310)	(42,523)	(39,237)
Proceeds from issuance of Senior Notes due 2025	0	246,937	0
Redemption of Senior Notes due 2016	0	(127,292)	0
Maturity of Senior Notes due 2015	0	(75,000)	0
Principal repayment on Bank Credit Facility	0	(38,000)	0
Exercise of stock options	3,329	1,629	8,252
Net cash used in financing activities	119,103	212,640	337,068
Net decrease in cash	1,161	3,834	(6,514)
Cash at beginning of period	15,509	11,675	18,189
Cash at end of period	16,670	15,509	11,675
Parent Company [Member]
Cash flows - operating activities
Interest expense paid	(11,754)	(13,521)	(13,902)
Federal income taxes recovered	8,914	8,413	10,030
Cash dividends received from subsidiaries	59,600	50,000	46,000
Other, net, including settlement of payables to subsidiaries	(3,434)	(4,097)	(1,478)
Net cash provided by operating activities	53,326	40,795	40,650
Cash flows - investing activities
Net increase (decrease) in investments	9,161	15,402	(4,647)
Net cash provided by (used in) investing activities	9,161	15,402	(4,647)
Cash flows - financing activities
Dividends paid to shareholders	(44,310)	(42,523)	(39,237)
Proceeds from issuance of Senior Notes due 2025	0	246,937	0
Redemption of Senior Notes due 2016	0	(127,292)	0
Maturity of Senior Notes due 2015	0	(75,000)	0
Principal repayment on Bank Credit Facility	0	(38,000)	0
Acquisition of treasury stock	(21,513)	(21,950)	(5,411)
Exercise of stock options	3,329	1,629	8,252
Net cash used in financing activities	(62,494)	(56,199)	(36,396)
Net decrease in cash	(7)	(2)	(393)
Cash at beginning of period	75	77	470
Cash at end of period	$ 68	$ 75	$ 77