Regulatory Capital Requirements (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Northwest Bancshares, Inc.
Total capital (to risk weighted assets)
Actual Amount	$ 1,147,027,000	$ 1,117,979,000
Actual Ratio (as a percent)	22.46%	21.53%
Tier I capital (to risk weighted assets)
Actual Amount	1,081,060,000	1,050,261,000
Actual Ratio (as a percent)	21.17%	20.22%
Tier I capital (leverage) (to total assets)
Actual Amount	1,081,060,000	1,050,261,000
Actual Ratio (as a percent)	13.87%	13.43%
Northwest Savings Bank
Regulatory Capital Requirements
Maximum amount available for dividend payments	47,500,000
Total capital (to risk weighted assets)
Actual Amount	946,531,000	875,676,000
Actual Ratio (as a percent)	18.60%	16.94%
Minimum Capital Requirements Amount	407,062,000	413,424,000
Minimum Capital Requirements Ratio (as a percent)	8.00%	8.00%
Well Capitalized Requirements Amount	508,828,000	516,780,000
Well Capitalized Requirements Ratio (as a percent)	10.00%	10.00%
Tier I capital (to risk weighted assets)
Actual Amount	882,234,000	810,727,000
Actual Ratio (as a percent)	17.34%	15.69%
Minimum Capital Requirements Amount	203,531,000	206,712,000
Minimum Capital Requirements Ratio (as a percent)	4.00%	4.00%
Well Capitalized Requirements Amount	305,297,000	310,068,000
Well Capitalized Requirements Ratio (as a percent)	6.00%	6.00%
Tier I capital (leverage) (to total assets)
Actual Amount	882,234,000	810,727,000
Actual Ratio (as a percent)	11.42%	10.41%
Minimum Capital Requirements Amount	309,127,000	311,473,000
Minimum Capital Requirements Ratio (as a percent)	4.00%	4.00%
Well Capitalized Requirements Amount	$ 386,408,000	$ 389,340,000
Well Capitalized Requirements Ratio (as a percent)	5.00%	5.00%