Business Combinations - Narrative - CBR Acquisition (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		4 Months Ended	12 Months Ended
	Aug. 17, 2015	Aug. 31, 2015	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Increase in goodwill							$ 296
Expected useful life						10 years 10 months
Net deferred tax liability						$ 23,927	197,066
Acquisition-related costs						$ 0	$ 0	$ 11,232
CBR
Business Acquisition [Line Items]
Cash consideration	$ 700,000
Increase in goodwill			$ 300	$ 1,800
Adjustment financial assets				1,900
Adjustment financial liabilities				500
Subsequent recognition of deferred tax asset				$ 600
Gross contractual amount of accounts receivable	11,700
Fair value accounts receivable	8,660
Net deferred tax liability	$ 144,800
Combined federal and state statutory income tax rate (percent)	37.00%
Deferred income tax liabilities	$ 149,873
Deferred tax assets	$ 5,062
Acquisition-related costs								11,200
Commitment fee								$ 6,800
Revenue of acquiree since acquisition					$ 24,100
CBR | Customer relationships
Business Acquisition [Line Items]
Expected useful life		20 years				20 years