Changes in Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in accumulated other comprehensive loss by component
Other comprehensive income (loss) before reclassifications			$ 237,421	$ (14,248)
Amounts reclassified from accumulated other comprehensive loss	$ 43,605	$ 80,908	152,169	265,147
Total other comprehensive income	234,144	94,528	389,590	250,899
Changes related to cash flow derivative hedges
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year			(820,850)	(1,232,073)
Other comprehensive income (loss) before reclassifications			230,341	(9,150)
Amounts reclassified from accumulated other comprehensive loss			151,319	263,774
Total other comprehensive income			381,660	254,624
Ending balance	(439,190)	(977,449)	(439,190)	(977,449)
Changes in defined benefit plans
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year			(28,083)	(26,447)
Other comprehensive income (loss) before reclassifications			(7,130)	(13,521)
Amounts reclassified from accumulated other comprehensive loss	293	285	850	1,373
Total other comprehensive income			(6,280)	(12,148)
Ending balance	(34,363)	(38,595)	(34,363)	(38,595)
Foreign currency translation adjustments
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year			(67,551)	(69,913)
Other comprehensive income (loss) before reclassifications			14,210	8,423
Amounts reclassified from accumulated other comprehensive loss			0	0
Total other comprehensive income			14,210	8,423
Ending balance	(53,341)	(61,490)	(53,341)	(61,490)
Accumulated other comprehensive loss
Changes in accumulated other comprehensive loss by component
Accumulated comprehensive loss at beginning of the year			(916,484)	(1,328,433)
Ending balance	$ (526,894)	$ (1,077,534)	$ (526,894)	$ (1,077,534)