Schedule II - Condensed Financial Information of Registrant (Parent Company Only) (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Debt securities	$ 605,746	$ 597,457
Cash and cash equivalents	64,982	79,632	$ 114,446	$ 130,985
Investment in subsidiaries	1,702	1,702
Deferred federal income taxes	1,937	1,365
Federal income tax recoverable	7,532	3,951
Other assets	13,856	13,801
Total assets	1,231,126	1,162,460
LIABILITIES AND STOCKHOLDERS' EQUITY
Revolving credit facility payable	30,000	30,000
Subordinated debt securities	55,753	55,701
Accounts payable and other accrued expenses	28,933	25,296
Total liabilities	980,008	896,724
Stockholders' equity:
Common stock, $.18 par value, authorized 33,333,333 shares; issued 20,872,831 shares in 2017 and 2016	3,757	3,757
Capital in excess of par value	123,180	123,166
Retained earnings	136,474	148,027
Accumulated other comprehensive income	12,234	10,371
Treasury stock (2,703,803 shares in 2017 and 2,260,849 in 2016), at cost	(24,527)	(19,585)
Total stockholders equity	251,118	265,736	262,026	252,037
Total liabilities and stockholders' equity	1,231,126	1,162,460
Parent Company [Member]
ASSETS
Debt securities	150
Cash and cash equivalents	12,194	9,034	$ 8,014	$ 11,839
Investment in subsidiaries	344,496	363,078
Deferred federal income taxes	493	333
Federal income tax recoverable	3,914	2,756
Other assets	3,571	3,878
Total assets	364,818	379,079
LIABILITIES AND STOCKHOLDERS' EQUITY
Revolving credit facility payable	30,000	30,000
Subordinated debt securities	55,753	55,701
Accounts payable and other accrued expenses	27,947	27,642
Total liabilities	113,700	113,343
Stockholders' equity:
Common stock, $.18 par value, authorized 33,333,333 shares; issued 20,872,831 shares in 2017 and 2016	3,757	3,757
Capital in excess of par value	123,180	123,166
Retained earnings	136,474	148,027
Accumulated other comprehensive income	12,234	10,371
Treasury stock (2,703,803 shares in 2017 and 2,260,849 in 2016), at cost	(24,527)	(19,585)
Total stockholders equity	251,118	265,736
Total liabilities and stockholders' equity	$ 364,818	$ 379,079