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Short-Term Borrowings (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Short-term Debt [Line Items] |  |  |
Balance at year-end | $ 719,123 | $ 681,703 |
FHLB, unused lines of credit available for short-term financing | 2,000,000 | 1,900,000 |
Federal Funds Purchased [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Balance at year-end | 60,000 | 50,000 | $ 99,500
Average during the year | 54,162 | 65,257 | 97,424
Maximum month end balance | $ 80,000 | $ 85,000 | $ 159,000
Weighted average rate during the year | 2.16% | 0.98% | 0.36%
Weighted average rate at December 31 | 2.41% | 1.19% | 0.51%
Securities Sold Under Repurchase Agreements [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Balance at year-end | $ 182,123 | $ 173,703 | $ 167,981
Average during the year | 175,539 | 168,821 | 162,201
Maximum month end balance | $ 190,326 | $ 189,875 | $ 178,326
Weighted average rate during the year | 0.07% | 0.06% | 0.06%
Weighted average rate at December 31 | 0.07% | 0.07% | 0.06%
Other Short-Term Borrowings [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Balance at year-end | $ 477,000 | $ 458,000 | $ 175,000
Average during the year | 460,334 | 263,575 | 80,260
Maximum month end balance | $ 591,000 | $ 424,000 | $ 175,000
Weighted average rate during the year | 1.02% | 0.59% | 0.42%
Weighted average rate at December 31 | 1.18% | 0.70% | 0.56%

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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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