Regulatory Capital (Tables)

3 Months Ended

Mar. 31, 2013

Banking and Thrift [Abstract]

Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations

Actual capital amounts and ratios and selected minimum regulatory thresholds for the Company and its bank subsidiary, First Interstate Bank (“FIB”), as of March 31, 2013 and December 31, 2012 are presented in the following tables:

	Actual				Adequately Capitalized				Well Capitalized
	Amount		Ratio		Amount		Ratio		Amount		Ratio
March 31, 2013
Total risk-based capital:
Consolidated	$	766,478	15.9	%	$	385,443	8.0	%	NA		NA
FIB	707,053		14.7		383,593		8.0		$	479,491	10.0	%
Tier 1 risk-based capital:
Consolidated	677,787		14.1		192,721		4.0		NA		NA
FIB	634,648		13.2		191,796		4.0		$	287,695	6.0
Leverage capital ratio:
Consolidated	677,787		9.2		293,323		4.0		NA		NA
FIB	634,648		8.7		292,739		4.0		$	365,924	5.0

	Actual				Adequately Capitalized				Well Capitalized
	Amount		Ratio		Amount		Ratio		Amount		Ratio
December 31, 2012
Total risk-based capital:
Consolidated	$	748,431	15.6	%	$	384,014	8.0	%	NA		NA
FIB	697,695		14.6		382,245		8.0		$	477,806	10.0	%
Tier 1 risk-based capital:
Consolidated	652,929		13.6		192,007		4.0		NA		NA
FIB	622,466		13.0		191,122		4.0		$	286,683	6.0
Leverage capital ratio:
Consolidated	652,929		8.8		296,559		4.0		NA		NA
FIB	622,466		8.4		296,061		4.0		$	370,077	5.0