Income Taxes - Reconciliations Valuation Allowance on Deferred Tax Assets (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 1,154,008	$ 1,092,951	$ 994,434
Additions: charges to bad debt expense	(33,044)	45,972	157,960
Additions: charges to other accounts	0	15,085	0
Deductions	(374,129)	0	(59,443)
Balance at end of period	$ 746,835	$ 1,154,008	$ 1,092,951