Subordinated Debentures (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Terms of Subordinated Debentures
Balance	$ 125,991	$ 125,848
First Company Statutory Trust 2001
Terms of Subordinated Debentures
Balance	$ 3,207
Rate at December 31, 2016	4.187%
Variable Rate Structure	3 mo LIBOR plus 3.30%
LIBOR Rate Spread	3.30%
Maturity Date	Jul. 31, 2031
First Company Statutory Trust 2003
Terms of Subordinated Debentures
Balance	$ 2,361
Rate at December 31, 2016	4.247%
Variable Rate Structure	3 mo LIBOR plus 3.25%
LIBOR Rate Spread	3.25%
Maturity Date	Mar. 26, 2033
Glacier Capital Trust II
Terms of Subordinated Debentures
Balance	$ 46,393
Rate at December 31, 2016	3.63%
Variable Rate Structure	3 mo LIBOR plus 2.75%
LIBOR Rate Spread	2.75%
Maturity Date	Apr. 07, 2034
Citizens (ID) Statutory Trust I
Terms of Subordinated Debentures
Balance	$ 5,155
Rate at December 31, 2016	3.643%
Variable Rate Structure	3 mo LIBOR plus 2.65%
LIBOR Rate Spread	2.65%
Maturity Date	Jun. 17, 2034
Glacier Capital Trust III
Terms of Subordinated Debentures
Balance	$ 36,083
Rate at December 31, 2016	2.17%
Variable Rate Structure	3 mo LIBOR plus 1.29%
LIBOR Rate Spread	1.29%
Maturity Date	Apr. 07, 2036
Glacier Capital Trust IV
Terms of Subordinated Debentures
Balance	$ 30,928
Rate at December 31, 2016	2.533%
Variable Rate Structure	3 mo LIBOR plus 1.57%
LIBOR Rate Spread	1.57%
Maturity Date	Sep. 15, 2036
Bank of the San Juans Bancorporation Trust I
Terms of Subordinated Debentures
Balance	$ 1,864
Rate at December 31, 2016	2.751%
Variable Rate Structure	3 mo LIBOR plus 1.82%
LIBOR Rate Spread	1.82%
Maturity Date	Mar. 01, 2037

Terms of subordinated debentures.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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