as of december 31 , 2017 , the company had gross state income tax credit carry-forwards of approximately $ 20 million , which expire from 2018 through 2020 . a deferred tax asset of approximately $ 16 million ( net of federal benefit ) has been established related to these state income tax credit carry-forwards , with a valuation allowance of $ 7 million against such deferred tax asset as of december 31 , 2017 . the company had a gross state net operating loss carry-forward of $ 39 million , which expires in 2027 . a deferred tax asset of approximately $ 3 million ( net of federal benefit ) has been established for the net operating loss carry-forward , with a full valuation allowance as of december 31 , 2017 . other state and foreign net operating loss carry-forwards are separately and cumulatively immaterial to the company 2019s deferred tax balances and expire between 2026 and 2036 . 14 . debt long-term debt consisted of the following: .

december 31 2017: senior notes due december 15 2021 5.000% ( 5.000 % ): 2014
senior notes due november 15 2025 5.000% ( 5.000 % ): 600
senior notes due december 1 2027 3.483% ( 3.483 % ): 600
mississippi economic development revenue bonds due may 1 2024 7.81% ( 7.81 % ): 84
gulf opportunity zone industrial development revenue bonds due december 1 2028 4.55% ( 4.55 % ): 21
less unamortized debt issuance costs: -26
total long-term debt: 1279
december 31 2016: senior notes due december 15 2021 5.000% ( 5.000 % ): 600
senior notes due november 15 2025 5.000% ( 5.000 % ): 600
senior notes due december 1 2027 3.483% ( 3.483 % ): 2014
mississippi economic development revenue bonds due may 1 2024 7.81% ( 7.81 % ): 84
gulf opportunity zone industrial development revenue bonds due december 1 2028 4.55% ( 4.55 % ): 21
less unamortized debt issuance costs: -27
total long-term debt: 1278

credit facility - in november 2017 , the company terminated its second amended and restated credit agreement and entered into a new credit agreement ( the "credit facility" ) with third-party lenders . the credit facility includes a revolving credit facility of $ 1250 million , which may be drawn upon during a period of five years from november 22 , 2017 . the revolving credit facility includes a letter of credit subfacility of $ 500 million . the revolving credit facility has a variable interest rate on outstanding borrowings based on the london interbank offered rate ( "libor" ) plus a spread based upon the company's credit rating , which may vary between 1.125% ( 1.125 % ) and 1.500% ( 1.500 % ) . the revolving credit facility also has a commitment fee rate on the unutilized balance based on the company 2019s leverage ratio . the commitment fee rate as of december 31 , 2017 was 0.25% ( 0.25 % ) and may vary between 0.20% ( 0.20 % ) and 0.30% ( 0.30 % ) . the credit facility contains customary affirmative and negative covenants , as well as a financial covenant based on a maximum total leverage ratio . each of the company's existing and future material wholly owned domestic subsidiaries , except those that are specifically designated as unrestricted subsidiaries , are and will be guarantors under the credit facility . in july 2015 , the company used cash on hand to repay all amounts outstanding under a prior credit facility , including $ 345 million in principal amount of outstanding term loans . as of december 31 , 2017 , $ 15 million in letters of credit were issued but undrawn , and the remaining $ 1235 million of the revolving credit facility was unutilized . the company had unamortized debt issuance costs associated with its credit facilities of $ 11 million and $ 8 million as of december 31 , 2017 and 2016 , respectively . senior notes - in december 2017 , the company issued $ 600 million aggregate principal amount of unregistered 3.483% ( 3.483 % ) senior notes with registration rights due december 2027 , the net proceeds of which were used to repurchase the company's 5.000% ( 5.000 % ) senior notes due in 2021 in connection with the 2017 redemption described below . in november 2015 , the company issued $ 600 million aggregate principal amount of unregistered 5.000% ( 5.000 % ) senior notes due november 2025 , the net proceeds of which were used to repurchase the company's 7.125% ( 7.125 % ) senior notes due in 2021 in connection with the 2015 tender offer and redemption described below . interest on the company's senior notes is payable semi-annually . the terms of the 5.000% ( 5.000 % ) and 3.483% ( 3.483 % ) senior notes limit the company 2019s ability and the ability of certain of its subsidiaries to create liens , enter into sale and leaseback transactions , sell assets , and effect consolidations or mergers . the company had unamortized debt issuance costs associated with the senior notes of $ 15 million and $ 19 million as of december 31 , 2017 and 2016 , respectively. .

Questions:
what was the change in the unamortized debt issuance costs associated with the senior notes from 2016 to 2017?
and how much does this change represent in relation to those costs in 2016, in percentage?

Answers:
-4
-21.1%