Pensions and Other Post-Employment Benefits (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Net benefit cost
Service cost	$ 8,760	$ 8,060	$ 9,195
Interest cost	9,949	10,820	10,446
Expected return on plan assets	(14,933)	(14,241)	(13,611)
Amortization of prior service cost (benefit)	(274)	(460)	(450)
Recognized net actuarial loss	6,636	6,005	7,537
Net periodic cost	10,138	10,184	13,117
Settlements	0	120	0
Total net benefit cost	10,138	10,304	13,117
Change in other comprehensive income
OCI at beginning of year	121,329	112,518	121,341
Increase (decrease) in OCI:
Recognized during year — prior service cost (credit)	274	460	450
Recognized during year — net actuarial (losses) gains	(6,636)	(6,005)	(7,537)
Occurring during year — prior service cost	3,804	0	0
Occurring during year — net actuarial losses (gains)	4,055	14,279	(1,697)
Other adjustments	0	120	0
Foreign currency exchange rate changes	(24)	(43)	(39)
OCI at end of year	122,802	121,329	112,518
Other Benefits
Net benefit cost
Service cost	91	105	115
Interest cost	398	562	554
Expected return on plan assets	0	0	0
Amortization of prior service cost (benefit)	(1,497)	(1,497)	(1,497)
Recognized net actuarial loss	0	0	0
Net periodic cost	(1,008)	(830)	(828)
Settlements	0	0	0
Total net benefit cost	(1,008)	(830)	(828)
Change in other comprehensive income
OCI at beginning of year	(9,961)	(11,267)	(12,261)
Increase (decrease) in OCI:
Recognized during year — prior service cost (credit)	1,497	1,497	1,497
Recognized during year — net actuarial (losses) gains	0	0	0
Occurring during year — prior service cost	0	0	0
Occurring during year — net actuarial losses (gains)	444	(191)	(503)
Other adjustments	0	0	0
Foreign currency exchange rate changes	0	0	0
OCI at end of year	$ (8,020)	$ (9,961)	$ (11,267)