Investment Securities (Summary of Amortized Cost and Fair Value of Held-to-Maturity Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment Securities Held-to-Maturity
Amortized Cost	$ 623,427	$ 509,971
Unrecognized Gains	2,648	7,446
Unrecognized Losses	17,544	4,712
Held-to-maturity, fair value	608,531	512,705
State and political subdivisions
Investment Securities Held-to-Maturity
Amortized Cost	622,927	509,471
Unrecognized Gains	2,648	7,446
Unrecognized Losses	17,354	4,512
Held-to-maturity, fair value	608,221	512,405
Trust preferred securities
Investment Securities Held-to-Maturity
Amortized Cost	500	500
Unrecognized Gains	0	0
Unrecognized Losses	190	200
Held-to-maturity, fair value	$ 310	$ 300

Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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- Definition

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

+ References

+ Details

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- Definition

Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

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- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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