Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt securities, available-for-sale, cost (in dollars)	$ 597,784	$ 538,629
Equity securities, available for sale, cost (in dollars)	31,449	24,524
Other investments, available-for-sale, cost (in dollars)	632,996	563,580
Unamortized debt issuance cost (in dollars)	$ 1,001	$ 1,053
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	2,260,849	1,775,512
Other Investments [Member]
Other investments, available-for-sale, cost (in dollars)	$ 3,763	$ 427