Schedule II Condensed Financial Information of Registrant (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows - operating activities
Interest expense paid	$ (13,521)	$ (13,902)	$ (13,825)
Federal income taxes recovered	24,861	29,195	33,672
Other, net, including settlement of payables to subsidiaries	(6,101)	(17,437)	(19,238)
Net cash provided by operating activities	207,043	221,933	205,936
Cash flows - investing activities
Net cash provided by (used in) investing activities	(415,849)	(565,515)	(598,326)
Cash flows - financing activities
Dividends paid to shareholders	(42,523)	(39,237)	(32,550)
Proceeds from issuance of Senior Notes due 2025	246,937	0	0
Redemption of Senior Notes due 2016	127,292	0	0
Maturity of Senior Notes due 2015	(75,000)	0	0
Principal repayment on Bank Credit Facility	(38,000)	0	0
Exercise of stock options	1,629	8,252	19,336
Net cash used in financing activities	212,640	337,068	395,398
Net increase (decrease) in cash	3,834	(6,514)	3,008
Cash at beginning of period	11,675	18,189	15,181
Cash at end of period	15,509	11,675	18,189
Parent Company [Member]
Cash flows - operating activities
Interest expense paid	(13,521)	(13,902)	(13,825)
Federal income taxes recovered	6,539	8,740	5,996
Cash dividends received from subsidiaries	50,000	46,000	41,000
Other, net, including settlement of payables to subsidiaries	(2,223)	(188)	(21,235)
Net cash provided by operating activities	40,795	40,650	11,936
Cash flows - investing activities
Net (increase) decrease in investments	15,402	(4,647)	5,488
Net cash provided by (used in) investing activities	15,402	(4,647)	5,488
Cash flows - financing activities
Dividends paid to shareholders	(42,523)	(39,237)	(32,550)
Proceeds from issuance of Senior Notes due 2025	246,937	0	0
Redemption of Senior Notes due 2016	(127,292)	0	0
Maturity of Senior Notes due 2015	(75,000)	0	0
Principal repayment on Bank Credit Facility	(38,000)	0	0
Acquisition of treasury stock	(21,950)	(5,411)	(3,889)
Exercise of stock options	1,629	8,252	19,336
Net cash used in financing activities	(56,199)	(36,396)	(17,103)
Net increase (decrease) in cash	(2)	(393)	321
Cash at beginning of period	77	470	149
Cash at end of period	$ 75	$ 77	$ 470