Nature of Operations and Summary of Significant Accounting Policies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Nature of Operations and Summary of Significant Accounting Policies
Number of Bank Divisions	13
Number of Operating Segments	1
Assets	$ 8,306,507,000	$ 7,884,350,000
Gross Loans	4,488,095,000	4,062,838,000
Maximum Period of Original Maturity to be Included in Cash and Cash Equivalents	3 months
Minimum period past due to consider loan as delinquent	30 days
Minimum period past due to consider loan as non accrual	90 days
Minimum number of days delinquent to charge off consumer loans	120 days
Maximum period up to which purchase price of business is allocated to assets acquired and liabilities assumed	1 year
Number of Reporting Units Subsequent to Aggregation for Goodwill Assessment	1
Bank Owned Life Insurance	46,030,000	37,617,000
Percentage of likelihood for term more likely than not	50.00%
Number of Steps to Achieve Core Revenue Recognition Principal	5
Minimum Range
Nature of Operations and Summary of Significant Accounting Policies
Number of years for home equity loan origination term	10 years
Minimum Range | Office Buildings
Nature of Operations and Summary of Significant Accounting Policies
Useful life of premises and equipment	15 years
Minimum Range | Furniture, fixtures and equipment
Nature of Operations and Summary of Significant Accounting Policies
Useful life of premises and equipment	3 years
Maximum Range
Nature of Operations and Summary of Significant Accounting Policies
Number of years for home equity loan origination term	15 years
Maximum Range | Office Buildings
Nature of Operations and Summary of Significant Accounting Policies
Useful life of premises and equipment	40 years
Maximum Range | Furniture, fixtures and equipment
Nature of Operations and Summary of Significant Accounting Policies
Useful life of premises and equipment	10 years
Montana Community Banks, Inc.
Nature of Operations and Summary of Significant Accounting Policies
Assets	175,041,000
Gross Loans	92,952,000
Deposits	$ 149,544,000