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Investments - Additional Information (Details) $ in Thousands	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Investment Holdings [Line Items]
Amortized Cost	$ 211,406	$ 196,402
Par value of mortgage-backed securities pledged to FRB	188,000	188,300
Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	$ 196,406	$ 196,402
Number of mortgage-backed securities with unrealized losses | security	48	35
Number of mortgage-backed securities | security	84	74
Utah Housing Corporation bonds
Investment Holdings [Line Items]
Amortized Cost	$ 15,000
Ginnie Mae | Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	$ 101,200
Number of mortgage-backed securities with unrealized losses | security	21	14
Fannie Mae | Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	$ 66,500
Freddie Mac | Mortgage-backed securities
Investment Holdings [Line Items]
Amortized Cost	28,800
Aa3 Rating | Utah Housing Corporation bonds
Investment Holdings [Line Items]
Amortized Cost	$ 15,000

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Number of Mortgage-Backed securities with unrealized losses

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Par Value of Mortgage-backed securities pledged to FRB

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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