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Borrowings - Long Term Borrowings (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Line of Credit Facility [Line Items] |  |
Long-term borrowings | $ 3,275,270 | $ 2,167,979
Weighted Average Interest Rate | 2.71% | 2.15%
Average Balance | $ 2,843,593 | $ 1,236,045
Floating rate borrowings |  |
Line of Credit Facility [Line Items] |  |
Long-term borrowings | $ 1,512,970 | $ 1,175,819
Weighted Average Interest Rate | 2.32% | 1.71%
Average Balance | $ 1,422,856 | $ 687,580
Fixed rate borrowings |  |
Line of Credit Facility [Line Items] |  |
Long-term borrowings | $ 1,762,300 | $ 992,160
Weighted Average Interest Rate | 3.04% | 2.68%
Average Balance | $ 1,420,737 | $ 548,465

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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + 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(a)(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 Reference 3: 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)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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