Segment Information (Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets	$ 5,220,137	$ 5,466,900	$ 5,938,419
Cash and cash equivalents	921,450	924,442
Short-term investments	18,974	115,879
Long-term investments	364,212	238,882
Identifiable long-lived assets	631,631	618,154	597,283
United States
Segment Reporting Information [Line Items]
Identifiable long-lived assets	613,990	596,694	577,260
Outside United States
Segment Reporting Information [Line Items]
Identifiable long-lived assets	17,641	21,460	20,023
Commerce Services | Global Ecommerce
Segment Reporting Information [Line Items]
Assets	994,554	1,102,313	1,023,732
Commerce Services | Presort Services
Segment Reporting Information [Line Items]
Assets	523,690	524,817	431,512
Operating Segments
Segment Reporting Information [Line Items]
Assets	3,583,637	3,779,864	3,781,041
Operating Segments | Commerce Services
Segment Reporting Information [Line Items]
Assets	1,518,244	1,627,130	1,455,244
Operating Segments | SendTech Solutions
Segment Reporting Information [Line Items]
Assets	2,065,393	2,152,734	2,325,797
Reconciling Items
Segment Reporting Information [Line Items]
Cash and cash equivalents	921,450	924,442	867,262
Short-term investments	18,974	115,879	59,391
Assets of discontinued operations	0	17,229	602,823
Long-term investments	364,212	238,882	269,374
Other corporate assets	$ 331,864	$ 390,604	$ 358,528