Summary of Significant Accounting Policies - Prepaid Expenses and Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Minimum percentage of current assets and liabilities required to be disclosed separately	5.00%
Prepaid expenses	$ 188,874	$ 184,374
Interest	71,176	76,615
Payroll and vacation	67,379	68,067
Incentive compensation	72,006	70,117
Accrued Dividends	172,102	5,625
Other	270,483	229,833
Accrued expenses	$ 653,146	$ 450,257