Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 2,000	$ 1,300	$ 5,200	$ 3,900
Goodwill [Line Items]
Goodwill	236,335	$ 191,371	236,335	$ 191,371	$ 191,371	$ 191,307
Non Strategic
Goodwill [Line Items]
Gross goodwill	200,000		200,000		200,000
Accumulated impairments	114,100		114,100		114,100
Accumulated divestiture related write-offs	85,900		85,900		85,900
Goodwill	$ 0		$ 0		$ 0