CONDENSED CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Available-for-sale securities, at amortized cost	$ 1,318,416	$ 1,293,239
Equity securities, at amortized cost	$ 930,000	$ 915,000
Common Stock, par value (in dollars per share)	$ 0.1	$ 0.1
Common Stock, authorized (in shares)	25,000,000	25,000,000
Common Stock, issued (in shares)	14,943,857	15,014,499
Treasury stock, shares (in shares)	117,940	123,956