Changes in Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in accumulated other comprehensive loss by component
Amounts reclassified from accumulated other comprehensive loss	$ 15,257	$ 53,653
Total other comprehensive income	151,450	24,162
Changes related to cash flow derivative hedges
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year	(250,355)	(820,850)
Other comprehensive income (loss) before reclassifications	127,616	(30,929)
Amounts reclassified from accumulated other comprehensive loss	14,914	53,390
Total other comprehensive income	142,530	22,461
Ending balance	(107,825)	(798,389)
Changes in defined benefit plans
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year	(33,666)	(28,083)
Other comprehensive income (loss) before reclassifications	7,417	(904)
Amounts reclassified from accumulated other comprehensive loss	343	263
Total other comprehensive income	7,760	(641)
Ending balance	(25,906)	(28,724)
Foreign currency translation adjustments
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year	(50,244)	(67,551)
Other comprehensive income (loss) before reclassifications	1,160	2,342
Amounts reclassified from accumulated other comprehensive loss	0	0
Total other comprehensive income	1,160	2,342
Ending balance	(49,084)	(65,209)
Accumulated other comprehensive loss
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year	(334,265)	(916,484)
Other comprehensive income (loss) before reclassifications	136,193	(29,491)
Amounts reclassified from accumulated other comprehensive loss	15,257	53,653
Total other comprehensive income	151,450	24,162
Ending balance	$ (182,815)	$ (892,322)