Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt securities, available-for-sale, cost (in dollars)	$ 550,268	$ 604,999
Equity securities, cost (in dollars)	68,709	30,253
Investments, available-for-sale, cost (in dollars)	622,740	639,015
Unamortized debt issuance cost (in dollars)	$ 898	$ 949
Common stock, par value (in dollars per share)	$ 0.18	$ 0.18
Common stock, authorized shares	33,333,333	33,333,333
Common stock, issued shares	20,872,831	20,872,831
Treasury stock, shares	2,846,131	2,703,803
Other Investments [Member]
Investments, available-for-sale, cost (in dollars)	$ 3,763	$ 3,763