Summary of Operating Lease Right-of-Use Assets and Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
ASSETS
Operating lease right-of-use assets	$ 35,896	$ 28,500
LIABILITIES
Operating lease liabilities, current (included in accrued and other liabilities)	$ 6,681
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	manh:AccruedAndOtherLiabilitiesCurrent
Operating lease liabilities, long-term	$ 32,416
Total operating lease liabilities	$ 39,097	$ 31,000