Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowances	$ 1,293	$ 353
Properties and equipment, accumulated depreciation	288,657	270,140
Identifiable intangible assets, accumulated amortization	$ 45,095	$ 37,620
Capital stock - authorized	80,000,000	80,000,000
Capital stock - par value	$ 1	$ 1
Capital stock - issued	36,137,463	35,810,528
Treasury stock	20,261,187	19,867,220