CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
NET INCOME	$ 40,776	$ 14,788	$ 51,963	$ 23,158
Pension and other postretirement benefit plans:
Net actuarial loss, net of tax of: (2018 – Three-month period $2,038, Nine-month period $689; 2017 – Three-month period $1,011, Nine-month period $2,010)	(5,877)	(1,589)	(1,987)	(3,158)
Pension settlement expense, net of tax of: (2018 – Three-month period $134, Nine-month period $413; 2017 – Three-month period $366, Nine-month period $1,417)	384	577	1,190	2,227
Amortization of unrecognized net periodic benefit costs, net of tax of: (2018 – Three-month period $146, Nine-month period $536; 2017 – Three-month period $331, Nine-month period $1,084)
Net actuarial loss	438	547	1,598	1,788
Prior service credit	(17)	(29)	(52)	(87)
Interest rate swap and foreign currency translation:
Change in unrealized income on interest rate swap, net of tax of: (2018 – Three-month period $59, Nine-month period $334; 2017 – Three-month period $16, Nine-month period $156)	167	25	946	241
Change in foreign currency translation, net of tax of: (2018 – Three-month period $45, Nine month-period $58; 2017 – Three-month period $190, Nine-month period $132)	127	294	(165)	205
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	(4,778)	(175)	1,530	1,216
TOTAL COMPREHENSIVE INCOME	$ 35,998	$ 14,613	$ 53,493	$ 24,374