Segment Information (Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 831,343	$ 790,125	$ 788,573	$ 795,084	$ 857,414	$ 760,281	$ 773,538	$ 820,289	$ 3,205,125	$ 3,211,522	$ 2,784,007
United States
Segment Reporting Information [Line Items]
Revenue									2,745,928	2,679,300	2,262,249
Outside United States
Segment Reporting Information [Line Items]
Revenue									459,197	532,222	521,758
Commerce Services
Segment Reporting Information [Line Items]
Total from contracts with customers									1,681,098	1,538,657	1,050,143
Commerce Services | Global Ecommerce
Segment Reporting Information [Line Items]
Total from contracts with customers									1,151,510	1,022,862	552,242
Commerce Services | Presort Services
Segment Reporting Information [Line Items]
Total from contracts with customers									529,588	515,795	497,901
SendTech Solutions
Segment Reporting Information [Line Items]
Total from contracts with customers									$ 1,524,027	$ 1,672,865	$ 1,733,864