Other Borrowings (Details) (USD $)
 9 Months Ended 9 Months Ended 9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Term note payable
quarterly_periods
Sep. 30, 2012
Term note payable
Intermountain statutory trust I trust preferred securities
Dec. 31, 2011
Term note payable
Intermountain statutory trust I trust preferred securities
Jan. 31, 2003
Term note payable
Intermountain statutory trust I trust preferred securities
Sep. 30, 2012
Term note payable
Intermountain statutory trust II trust preferred securities
Dec. 31, 2011
Term note payable
Intermountain statutory trust II trust preferred securities
Mar. 31, 2004
Term note payable
Intermountain statutory trust II trust preferred securities
Sep. 30, 2012
Interest rate swap
Term note payable
Debt Instrument [Line Items]                    
Other borrowings $ 16,527,000 $ 16,527,000   $ 8,279,000 [1] $ 8,279,000 [1]   $ 8,248,000 [2] $ 8,248,000 [2]    
Debt Issuance           8,000,000     8,000,000  
Description of variable rate basis       90-day LIBOR     90-day LIBOR      
Basis spread on variable rate       3.25%     2.80%      
Interest rate at period end       3.62%     3.26%      
Derivative, notional amount                   $ 8,200,000
Derivative, fixed interest rate                   7.38%
Derivative term of agreement                   5 years
Debt instrument number of interest payment deferral periods     20              
[1] In January 2003, the Company issued $8.0 million of Trust Preferred securities through its subsidiary, Intermountain Statutory Trust I. The debt associated with these securities bears interest on a variable basis tied to the 90-day LIBOR (London Inter-Bank Offering Rate) index plus 3.25%, with interest only paid quarterly. The rate on this borrowing was 3.62% at September 30, 2012. The debt is callable by the Company quarterly and matures in March 2033. See Note A and B below.
[2] In March 2004, the Company issued $8.0 million of Trust Preferred securities through its subsidiary, Intermountain Statutory Trust II. The debt associated with these securities bears interest on a variable basis tied to the 90-day LIBOR index plus 2.8%, with interest only paid quarterly. The rate on this borrowing was 3.26% at September 30, 2012. The debt is callable by the Company quarterly and matures in April 2034. During the third quarter of 2008, the Company entered into an interest rate swap contract with Pacific Coast Bankers Bank. The purpose of the $8.2 million notional value swap is to convert the variable rate payments made on our Trust Preferred I obligation to a series of fixed rate payments at 7.38% for five years, as a hedging strategy to help manage the Company’s interest-rate risk. See Note A and B below:A)Intermountain’s obligations under the debentures issued to the trusts referred to above constitute a full and unconditional guarantee by Intermountain of the Statutory Trusts’ obligations under the Trust Preferred Securities. In accordance with ASC 810, Consolidation, the trusts are not consolidated and the debentures and related amounts are treated as debt of Intermountain.B)To conserve the liquid assets of the parent Company, the Company’s Board of Directors decided to defer regularly scheduled interest payments on its outstanding Junior Subordinated Debentures related to its Trust Preferred Securities (“TRUPS Debentures”) beginning in December 2009. The Company is permitted to defer payments of interest on the TRUPS Debentures for up to 20 consecutive quarterly periods without default. During the deferral period, the Company may not pay any dividends or distributions on, or redeem, purchase or acquire, or make a liquidation payment with respect to the Company’s capital stock, or make any payment of principal or interest on, or repay, repurchase or redeem any debt securities of the Company that rank equally or junior to the TRUPS Debentures. In light of the Company's recent capital raise and improved financial performance, the Company now anticipates paying the deferred interest on the TRUPS as early as the fourth quarter of 2012.