Regulatory Capital (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Total capital (to risk-weighted assets)
Actual, amount	$ 1,900,621	$ 1,661,249
Actual, ratio	0.1463	0.1495
Minimum capital requirement, amount	$ 1,039,094	$ 888,986
Minimum capital requirement, ratio	0.0800	0.0800
Tier 1 capital (to risk-weighted assets)
Actual, amount	$ 1,613,066	$ 1,528,683
Actual, ratio	0.1242	0.1376
Minimum capital requirement, amount	$ 779,321	$ 666,740
Minimum capital requirement, ratio	0.0600	0.0600
Common Equity Tier 1 (to risk-weighted assets)
Actual, amount	$ 1,613,066	$ 1,398,183
Actual, ratio	0.1242	0.1258
Minimum capital requirement, amount	$ 584,491	$ 500,055
Minimum capital requirement, ratio	4.50%	4.50%
Tier 1 capital (to average assets)
Actual, amount	$ 1,613,066	$ 1,528,683
Actual, ratio	0.0912	0.1165
Minimum capital requirement, amount	$ 707,823	$ 524,987
Minimum capital requirement, ratio	0.0400	0.0400
Total stockholders’ equity	$ 2,307,041	$ 1,960,733	$ 1,515,854	$ 1,199,057
Glacier Bank
Total capital (to risk-weighted assets)
Actual, amount	$ 1,824,269	$ 1,625,527
Actual, ratio	0.1406	0.1464
Minimum capital requirement, amount	$ 1,038,148	$ 888,110
Minimum capital requirement, ratio	0.0800	0.0800
Well capitalized requirement, amount	$ 1,297,686	$ 1,110,137
Well capitalized requirement, ratio	0.1000	0.1000
Tier 1 capital (to risk-weighted assets)
Actual, amount	$ 1,674,714	$ 1,500,461
Actual, ratio	0.1291	0.1352
Minimum capital requirement, amount	$ 778,611	$ 666,082
Minimum capital requirement, ratio	0.0600	0.0600
Well capitalized requirement, amount	$ 1,038,148	$ 888,110
Well capitalized requirement, ratio	0.0800	0.0800
Common Equity Tier 1 (to risk-weighted assets)
Actual, amount	$ 1,674,714	$ 1,500,461
Actual, ratio	0.1291	0.1352
Minimum capital requirement, amount	$ 583,959	$ 499,562
Minimum capital requirement, ratio	4.50%	4.50%
Well capitalized requirement, amount	$ 843,496	$ 721,589
Well capitalized requirement, ratio	6.50%	6.50%
Tier 1 capital (to average assets)
Actual, amount	$ 1,674,714	$ 1,500,461
Actual, ratio	0.0956	0.1150
Minimum capital requirement, amount	$ 700,529	$ 522,040
Minimum capital requirement, ratio	0.0400	0.0400
Well capitalized requirement, amount	$ 875,662	$ 652,550
Well capitalized requirement, ratio	0.0500	0.0500