Changes in Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in accumulated other comprehensive loss by component
Other comprehensive (loss) income before reclassifications	$ (29,491)	$ (96,808)
Amounts reclassified from accumulated other comprehensive loss	53,653	102,681
Total other comprehensive income	24,162	5,873
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 (loss) income before reclassifications	(30,929)	(99,659)
Amounts reclassified from accumulated other comprehensive loss	53,390	102,396
Total other comprehensive income	22,461	2,737
Ending balance	(798,389)	(1,229,336)
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 (loss) income before reclassifications	(904)	(3,797)
Amounts reclassified from accumulated other comprehensive loss	263	285
Total other comprehensive income	(641)	(3,512)
Ending balance	(28,724)	(29,959)
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 (loss) income before reclassifications	2,342	6,648
Amounts reclassified from accumulated other comprehensive loss	0	0
Total other comprehensive income	2,342	6,648
Ending balance	(65,209)	(63,265)
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	$ (892,322)	$ (1,322,560)