Investment Securities - Summary of Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	$ 16,176	$ 159,061
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9)	(1,551)
12 months or more, Fair Value	600,574	523,831
NBHC_AvailableForSaleSecuritiesDebtMaturitiesTwelveMonthsOrGreaterFairValue	600,574	523,831
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(14,435)	(19,360)
Total, Fair Value	616,750	682,892
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(14,444)	(20,911)
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	235	30,853
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(392)
12 months or more, Fair Value	86,197	69,169
NBHC_AvailableForSaleSecuritiesDebtMaturitiesTwelveMonthsOrGreaterFairValue	86,197	69,169
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(954)	(1,481)
Total, Fair Value	86,432	100,022
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(954)	(1,873)
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value	15,941	127,767
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9)	(1,150)
12 months or more, Fair Value	513,936	454,662
NBHC_AvailableForSaleSecuritiesDebtMaturitiesTwelveMonthsOrGreaterFairValue	513,936	454,662
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(13,472)	(17,879)
Total, Fair Value	529,877	582,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(13,481)	(19,029)
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months Fair Value		441
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(9)
12 months or more, Fair Value	441
NBHC_AvailableForSaleSecuritiesDebtMaturitiesTwelveMonthsOrGreaterFairValue	441
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(9)
Total, Fair Value	441	441
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (9)	$ (9)