Intangible Assets - Finite-Lived (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Intangible assets with finite lives
Accumulated Amortization	$ 238,618	$ 193,347
Weighted average
Intangible assets with finite lives
Amortization period	12 years 7 months 6 days	12 years 9 months 18 days
Customer relationships
Intangible assets with finite lives
Gross Carrying Amount	$ 653,531	$ 640,052
Accumulated Amortization	180,721	144,768
Net carrying amount	$ 472,810	$ 495,284
Customer relationships | Weighted average
Intangible assets with finite lives
Amortization period	13 years 6 months	13 years 8 months 12 days
Acquired software
Intangible assets with finite lives
Gross Carrying Amount	$ 88,710	$ 82,400
Accumulated Amortization	57,897	48,579
Net carrying amount	$ 30,813	$ 33,821
Acquired software | Weighted average
Intangible assets with finite lives
Amortization period	6 years 1 month 6 days	6 years 2 months 12 days