Regulatory Capital Requirements (Details) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Tier 1 capital (leverage to average assets)
Minimum capital requirements (as a percent)	2.50%	2.50%
Northwest Bank
Total capital (to risk weighted assets)
Actual amount	$ 1,568,202	$ 1,551,084
Actual ratio (as a percent)	0.14712	0.15738
Capital required for capital adequacy	$ 1,119,214	$ 1,034,819
Minimum capital requirements ratio (as a percent)	0.10500	0.10500
Well capitalized requirements amount	$ 1,065,918	$ 985,542
Well capitalized requirements ratio (as a percent)	0.10000	0.10000
Tier 1 capital (to risk weighted assets)
Actual amount	$ 1,452,962	$ 1,467,362
Actual ratio (as a percent)	0.13631	0.14889
Minimum capital requirements amount	$ 906,030	$ 837,711
Minimum capital requirements ratio	8.50%	8.50%
Well capitalized requirements amount	$ 852,734	$ 788,434
Well capitalized requirements ratio (as a percent)	0.08000	0.08000
CET 1 capital (to risk weighted assets)
Actual amount	$ 1,452,962	$ 1,467,362
Actual ratio (as a percent)	13.631%	14.889%
Minimum capital requirements amount	$ 746,143	$ 689,879
Minimum capital requirements ratio (as a percent)	7.00%	7.00%
Well capitalized requirements amount	$ 692,847	$ 640,602
Well capitalized requirements ratio (as a percent)	6.50%	6.50%
Tier 1 capital (leverage to average assets)
Actual ratio (as a percent)	0.10365	0.10296
Minimum capital requirements amount	$ 560,706	$ 570,047
Minimum capital requirements ratio (as a percent)	0.04000	0.04000
Well capitalized requirements amount	$ 700,882	$ 712,558
Well capitalized requirements ratio (as a percent)	0.05000	0.05000
Northwest Bancshares, Inc.
Total capital (to risk weighted assets)
Actual amount	$ 1,745,701	$ 1,682,487
Actual ratio (as a percent)	0.16363	0.17056
Capital required for capital adequacy	$ 1,120,216	$ 1,035,786
Minimum capital requirements ratio (as a percent)	0.10500	0.10500
Well capitalized requirements amount	$ 1,066,872	$ 986,463
Well capitalized requirements ratio (as a percent)	0.10000	0.10000
Tier 1 capital (to risk weighted assets)
Actual amount	$ 1,516,621	$ 1,475,190
Actual ratio (as a percent)	0.14216	0.14954
Minimum capital requirements amount	$ 906,841	$ 838,494
Minimum capital requirements ratio	8.50%	8.50%
Well capitalized requirements amount	$ 853,498	$ 789,170
Well capitalized requirements ratio (as a percent)	0.08000	0.08000
CET 1 capital (to risk weighted assets)
Actual amount	$ 1,391,296	$ 1,350,125
Actual ratio (as a percent)	13.041%	13.687%
Minimum capital requirements amount	$ 746,810	$ 690,524
Minimum capital requirements ratio (as a percent)	7.00%	7.00%
Well capitalized requirements amount	$ 693,467	$ 641,201
Well capitalized requirements ratio (as a percent)	6.50%	6.50%
Tier 1 capital (leverage to average assets)
Actual ratio (as a percent)	0.10817	0.10349
Minimum capital requirements amount	$ 560,816	$ 570,160
Minimum capital requirements ratio (as a percent)	0.04000	0.04000
Well capitalized requirements amount	$ 701,020	$ 712,699
Well capitalized requirements ratio (as a percent)	0.05000	0.05000