Note 12 - Associate Benefits (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	25.00%
Defined Contribution Plan, Maximum Percentage of Annual Contribution Employee Subject to Match	6.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	20.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 521,000	$ 447,000	$ 396,000

Maximum percentage of employee gross pay, by the terms of the plan, that the employer may apply a percentage match contribution to a defined contribution plan.

No definition available.

Name:	nrc_DefinedContributionPlanMaximumPercentageOfAnnualContributionEmployeeSubjectToMatch
Namespace Prefix:	nrc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration