Income Taxes - Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 68,034,000	$ 70,315,000	$ 66,088,000	$ 77,089,000
Additions based on tax positions related to the current year	14,466,000	7,929,000	17,131,000
Additions for tax positions of prior years	4,105,000	9,076,000	2,900,000
Reductions for tax positions of prior years	(9,653,000)	(3,067,000)	(17,135,000)
Settlements	(954,000)	(3,106,000)	(1,153,000)
Lapse of statutes	(10,245,000)	(6,605,000)	(12,744,000)
Unrecognized potential tax benefits that would impact effective tax rate	59,200,000
Potential interest and penalty expense (income)	(500,000)	700,000	$ (4,300,000)
Accrued interest and penalties	$ 16,500,000	14,600,000
Minimum [Member]
Income Tax Contingency [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound		0
Maximum [Member]
Income Tax Contingency [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound		$ 14,100,000