Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Services	$ 326,968	$ 344,700
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	21,276
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	348,244
United States
Disaggregation of Revenue [Line Items]
Services	256,524	274,682
United States | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	9,018
United States | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	265,542
Canada
Disaggregation of Revenue [Line Items]
Services	26,379	26,470
Canada | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	953
Canada | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	27,332
Other
Disaggregation of Revenue [Line Items]
Services	44,065	43,548
Other | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	11,305
Other | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	55,370
Food & Beverage
Disaggregation of Revenue [Line Items]
Services	64,285	62,273
Food & Beverage | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	6,805
Food & Beverage | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	71,090
Retail
Disaggregation of Revenue [Line Items]
Services	35,772	43,324
Retail | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	840
Retail | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	36,612
Consumer Products
Disaggregation of Revenue [Line Items]
Services	31,802	37,922
Consumer Products | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	132
Consumer Products | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	31,934
Communications
Disaggregation of Revenue [Line Items]
Services	29,657	35,728
Communications | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	3,311
Communications | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	32,968
Automotive
Disaggregation of Revenue [Line Items]
Services	20,494	32,354
Automotive | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	4,218
Automotive | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	24,712
Technology
Disaggregation of Revenue [Line Items]
Services	34,144	30,550
Technology | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	2,835
Technology | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	36,979
Healthcare
Disaggregation of Revenue [Line Items]
Services	33,170	28,069
Healthcare | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	968
Healthcare | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	34,138
Financials
Disaggregation of Revenue [Line Items]
Services	21,838	19,983
Financials | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	285
Financials | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	22,123
Transportation and Travel/Lodging
Disaggregation of Revenue [Line Items]
Services	14,848	13,213
Transportation and Travel/Lodging | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	697
Transportation and Travel/Lodging | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	15,545
Other
Disaggregation of Revenue [Line Items]
Services	40,958	$ 41,284
Other | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Services	1,185
Other | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of Revenue [Line Items]
Services	$ 42,143