Profit Interest Units of SIS Holdings LP - Award Activity (Details) - Class B Profit Interest Units - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of units
Outstanding, beginning balance (in shares)	253,384	261,759
Forfeited (in shares)	(3,348)	(8,375)
Outstanding, ending balance (in shares)	250,036	253,384
Weighted- average grant date fair value
Outstanding, beginning balance, weighted-average grant date fair value (in dollars per share)	$ 87.14	$ 87.12	$ 87.13
Forfeited, weighted-average grant date fair value (in dollars per share)	(85.94)	(87.32)
Outstanding, ending balance, weighted-average grant date fair value (in dollars per share)	$ 87.14	$ 87.12