Acquisitions and Other Investments - Goodwill Allocated to Segments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Oct. 15, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 1,228,422		$ 1,008,097	$ 989,685
Pinnacle
Business Acquisition [Line Items]
Goodwill		$ 219,531
Pinnacle | Northeast segment
Business Acquisition [Line Items]
Goodwill		56,400
Pinnacle | South segment
Business Acquisition [Line Items]
Goodwill		48,300
Pinnacle | West segment
Business Acquisition [Line Items]
Goodwill		51,431
Pinnacle | Midwest segment
Business Acquisition [Line Items]
Goodwill		$ 63,400