FLC OF AN MLG ACR ACFT MISUNDERSTOOD APCH CLRNC GIVEN BY ARTCC AND STARTED THE WRONG APCH. HDG TRACK DEV.

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FLYING AN MLG ACFT APCHING IDAHO FALLS VOR FOR LNDG AT IDA. WHILE UNDER CTL OF ZLC AT 14000 FT; WE WERE 3 MI S OF IDA VOR PROCEEDING N. ZLC CLRED US TO 'CROSS IDA VOR AT 10000 FT AND CLRED FOR ILS 20 APCH AT IDA.' DURING MY READBACK I STATED WE WOULD BE TIGHT ON XING AT 10000 FT AND UNDERSTAND CLRED ILS 20 AT IDA. CTR THEN CLARIFIED TO 'CROSS THE VOR 10000 FT OR ABOVE AND CLRED FOR THE APCH.' 'CONTACT IDA TWR ON 118.5' (THIS IS A NON RADAR ENVIRONMENT). WE READ IT BACK AND SWITCHED FREQS. BY NOW; WE WERE PAST THE VOR AND HEADED FOR UCONN OM FOR A PROC TURN. I CALLED IDA TWR AND RPTED UCONN OUTBOUND. TWR RESPONDED BY SAYING 'WERE YOU CLRED FOR THE ILS? IT'S INOP AND YOU SHOULD SHOOT THE VOR 20 APCH.' WE TURNED L AND CORRECTED COURSE FOR THE VOR 20 APCH AND COMPLETED THE PROC AND LNDG WITHOUT A PROB. THE ILS COURSE IS APPROX THE 023 DEG RADIAL FROM IDA VOR WHILE THE VOR COURSE IS 010 DEGS. THEREFORE; AT SOME POINT; WE WERE E OF THE DESIRED POS AND WE WENT LONG (ABOUT 12.5 DME) ON THE PROC TURN CORRECTING FROM 1 APCH TO THE OTHER. IT MAY HAVE BEEN A READBACK ERROR ON MY PART OR A WRONG CLRNC BY ZLC. IN EITHER CASE; AN EARLIER CLRNC WOULD HAVE HELPED SINCE WE COULD HAVE CONTACTED IDA TWR SOONER. THIS MAY HAVE PREVENTED US FROM COMMENCING THE INCORRECT APCH.