Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income, Net of Taxes	Retained Earnings	Treasury Stock
Balance at at Dec. 31, 2009	$ 620,435	$ 166	$ 144,814	$ 18,866	$ 506,301	$ (49,712)
Net income	56,342
Other comprehensive income, net of deferred federal income taxes	3,106
Resticted share awards issued	155	1	154
Recognition of employee share based compensation	3,933		3,933
Exercise of options, net of federal income taxes	2,417		2,416
Dividends paid	(27,098)				(27,098)
Acquisition of treasury stock	(5,814)					(5,814)
Balance at at Dec. 31, 2010	653,476	168	151,317	21,972	535,545	(55,526)
Net income	13,702				13,702
Other comprehensive income, net of deferred federal income taxes	13,649			13,649
Resticted share awards issued	189	1	188
Recognition of employee share based compensation	4,692
Exercise of options, net of federal income taxes	970		970
Dividends paid	(30,322)				(30,322)
Acquisition of treasury stock	(43)					(43)
Balance at at Dec. 31, 2011	656,313	169	157,167	35,621	518,925	(55,569)
Net income	58,070				58,070
Other comprehensive income, net of deferred federal income taxes	7,735			7,735
Resticted share awards issued	167	1	166
Recognition of employee share based compensation	4,484
Exercise of options, net of federal income taxes	1,224	1
Dividends paid	(33,634)				(33,634)
Balance at at Dec. 31, 2012	$ 694,359	$ 170	$ 163,041	$ 43,356	$ 543,361	$ (55,569)