Annual report pursuant to Section 13 and 15(d)

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details)

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ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Components of accumulated other comprehensive income (loss)      
Balance $ 653,924 $ 568,545 $ 524,029
Change during the period      
Other comprehensive earnings/(loss) (25,122) 24,119 1,103
Balance 711,908 653,924 568,545
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]      
Components of accumulated other comprehensive income (loss)      
Balance (35,041) (49,200)  
Change during the period      
Before-tax amount (14,812) 18,980  
Tax benefit 3,762 (4,821)  
Other comprehensive earnings/(loss) (11,050) 14,159  
Balance (46,091) (35,041) (49,200)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]      
Components of accumulated other comprehensive income (loss)      
Balance (10,915) (20,875)  
Change during the period      
Before-tax amount (14,072) 9,960  
Tax benefit  
Other comprehensive earnings/(loss) (14,072) 9,960  
Balance (24,987) (10,915) (20,875)
AOCI Attributable to Parent [Member]      
Components of accumulated other comprehensive income (loss)      
Balance (45,956) (70,075) (71,178)
Change during the period      
Before-tax amount (28,884) 28,940  
Tax benefit 3,762 (4,821)  
Other comprehensive earnings/(loss) (25,122) 24,119  
Balance $ (71,078) $ (45,956) $ (70,075)