CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowances (in dollars)	$ 8,057	$ 7,657
Other accounts receivable, allowances (in dollars)	$ 952	$ 921
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	70,000,000	70,000,000
Common stock, issued shares	28,541,578	28,495,628
Treasury stock, at cost, shares	2,857,460	2,851,578