Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 705,560	$ 983,202
Depreciation	105,868	72,159
Deferred revenue	57,541	52,693
Allowance for doubtful accounts	26,193	30,379
Deferred compensation	43,440	61,837
Unrealized loss	56,871	71,587
Nondeductible reserves	43,176	40,690
Interest	17,279	10,728
Total deferred tax assets	1,055,928	1,323,275
Deferred tax liabilities:
Investment in subsidiaries	115,886	107,400
Amortization of intangible assets	314,390	371,668
Other	1,026	153
Total deferred tax liabilities	431,302	479,221
Net deferred tax assets	624,626	844,054
Valuation allowance for net deferred tax assets	(746,835)	(1,154,008)
Net deferred tax liabilities	$ (122,209)	$ (309,954)