Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deposits [Abstract]
Prepaid health insurance	$ 9,000	$ 9,000
Deposits – health insurance	7,900	8,100
Deposits workers' compensation	186,331	175,913	$ 166,474	$ 154,215
Deposits and prepaid health insurance	$ 203,231	$ 193,013

Carrying amount as of the balance sheet date for portion of health insurance contract to be utilized over longer than one year, carrying value of amounts transferred to third party health care providers for security purposes that are expected to be returned or applied towards payment after one year or beyond the operating cycle, if longer and carrying value of amounts transferred to third party workers' compensation insurance providers for security purposes that are expected to be returned or applied towards payment after one year or beyond the operating cycle, if longer.

No definition available.

Name:	nsp_Depositsandprepaidhealthinsurance
Namespace Prefix:	nsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant