Segment Information (Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total from contracts with customers									$ 2,629,541
Revenue	$ 947,140	$ 832,856	$ 861,436	$ 880,948	$ 916,406	$ 733,273	$ 730,413	$ 743,180	3,522,380	$ 3,123,272	$ 2,981,323
United States
Segment Reporting Information [Line Items]
Revenue									2,865,228	2,466,403	2,299,607
Outside United States
Segment Reporting Information [Line Items]
Revenue									657,152	656,869	681,716
Global Ecommerce
Segment Reporting Information [Line Items]
Total from contracts with customers									1,022,862
Presort Services
Segment Reporting Information [Line Items]
Total from contracts with customers									515,795
North America Mailing
Segment Reporting Information [Line Items]
Total from contracts with customers									513,393
Revenue									1,275,025
International Mailing
Segment Reporting Information [Line Items]
Total from contracts with customers									236,636
Revenue									367,843
Commerce Services
Segment Reporting Information [Line Items]
Total from contracts with customers									1,538,657	1,050,143	814,902
Commerce Services | Global Ecommerce
Segment Reporting Information [Line Items]
Total from contracts with customers									1,022,862	552,242	339,320
Commerce Services | Presort Services
Segment Reporting Information [Line Items]
Total from contracts with customers									515,795	497,901	475,582
SMB Solutions
Segment Reporting Information [Line Items]
Total from contracts with customers									1,642,868	1,741,502	1,841,271
SMB Solutions | North America Mailing
Segment Reporting Information [Line Items]
Total from contracts with customers									1,275,025	1,357,405	1,429,027
SMB Solutions | International Mailing
Segment Reporting Information [Line Items]
Total from contracts with customers									367,843	384,097	412,244
Software Solutions
Segment Reporting Information [Line Items]
Total from contracts with customers									$ 340,855	$ 331,627	$ 325,150