Intangible Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 6,500,000	$ 1,200,000
Goodwill [Line Items]
Goodwill	1,398,501,000	$ 191,371,000	$ 1,386,853,000	$ 191,371,000
Non-Strategic
Goodwill [Line Items]
Gross goodwill	200,000,000		200,000,000
Accumulated impairments	114,100,000		114,100,000
Accumulated divestiture related write-offs	85,900,000		85,900,000
Goodwill	$ 0		$ 0