CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
NET INCOME	$ 71,100	$ 39,985	$ 67,262
Pension and other postretirement benefit plans:
Net actuarial gain (loss), net of tax of: (2020 - $513; 2019 - $2,308, 2018 - $477)	1,480	6,657	(1,376)
Pension settlement expense, including termination expense, net of tax of: (2020 - $23; 2019 - $1,167, 2018 - $3,327)	66	7,338	9,598
Amortization of unrecognized net periodic benefit cost (credit), net of tax of: (2020 - $152; 2019 - $314, 2018 - $740)
Net actuarial (gain) loss	(437)	931	2,204
Prior service credit	(1)	(25)	(69)
Interest rate swap and foreign currency translation:
Change in unrealized (loss) on interest rate swap, net of tax of: (2020 - $277; 2019 - $357)	(782)	(1,007)
Change in unrealized gain on interest rate swap, net of tax of:(2018 - $84)			236
Change in foreign currency translation, net of tax of: (2020 - $232; 2019 - $194, 2018 - $241)	661	547	(681)
OTHER COMPREHENSIVE INCOME, net of tax	987	14,441	9,912
TOTAL COMPREHENSIVE INCOME	$ 72,087	$ 54,426	$ 77,174