Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income, Net of Taxes	Retained Earnings	Treasury Stock	Total
Balance at Dec. 31, 2015	$ 174	$ 179,896	$ 16,464	$ 531,800	$ (83,835)	$ 644,499
Net income				34,035		34,035
Unrealized gains on securities available for sale, net of deferred federal income taxes			20,282			20,282
Restricted share awards issued		280				280
Recognition of employee share-based compensation, net of deferred federal income taxes		1,851				1,851
Exercise of options, net of federal income taxes		251				251
Dividends paid and accrued				(21,163)		(21,163)
Balance at Jun. 30, 2016	174	182,278	36,746	544,672	(83,835)	680,035
Balance at Dec. 31, 2016	174	184,549	15,843	553,995	(83,835)	670,726
Net income				33,124		33,124
Unrealized gains on securities available for sale, net of deferred federal income taxes			8,607			8,607
Restricted share awards issued	1	294				295
Recognition of employee share-based compensation, net of deferred federal income taxes		2,419				2,419
Dividends paid and accrued				(21,337)		(21,337)
Balance at Jun. 30, 2017	$ 175	$ 187,262	$ 24,450	$ 565,782	$ (83,835)	$ 693,834