Intangible Assets - Total by Major Asset Class (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Intangible assets
Gross carrying amount	$ 746,441	$ 726,652
Accumulated Amortization	238,618	193,347
Net carrying amount	507,823	533,305
Intangible assets, gross
Total intangible assets, gross	746,441	726,652
Intangible assets, net
Net carrying amount	$ 507,823	$ 533,305
Weighted average
Intangible assets
Amortization period	12 years 7 months 6 days	12 years 9 months 18 days