Assets and liabilities measured at fair value (Details) $ in Thousands	Jan. 31, 2020 USD ($)
Reported amount | Current portion of long-term debt obligations
Liabilities:
Long-term obligations	$ 555
Reported amount | Long-term obligations
Liabilities:
Long-term obligations	2,911,438
Reported amount | Accrued expenses and other current liabilities
Liabilities:
Deferred compensation	1,644
Reported amount | Noncurrent Other liabilities
Liabilities:
Deferred compensation	27,218
Fair value measurements on recurring basis | Balance at the end of the period
Liabilities:
Long-term obligations	3,142,019
Deferred compensation	28,862
Fair value measurements on recurring basis | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Liabilities:
Long-term obligations	2,711,924
Deferred compensation	28,862
Fair value measurements on recurring basis | Significant Other Observable Inputs (Level 2)
Liabilities:
Long-term obligations	$ 430,095