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Summary of Significant Accounting Policies - Income Per Share, Allowance for Doubful Accounts, Income Taxes, and Concentration of Credit Risk (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
bank
fund
$ / shares
shares
Sep. 30, 2017
USD ($)
$ / shares
shares
Sep. 30, 2018
USD ($)
bank
fund
$ / shares
shares
Sep. 30, 2017
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
bank
fund
Accounting Policies [Abstract]          
Concentration Risk, Number of "Triple A" Rated Money Market Funds | fund 0   0   12
Effective Income Tax Rate Reconciliation Repatriation Of Foreign Earnings, Cash And Liquid Assets         15.50%
Income (Loss) Per Share-Basic and Diluted          
Income (loss) from continuing operations $ 78,628 $ 25,382 $ 218,145 $ 167,374  
Less: Net (Loss) Income Attributable to Noncontrolling Interests (125) (21) 485 2,853  
Income (loss) from continuing operations (utilized in numerator of Earnings Per Share calculation) 78,753 25,403 217,660 164,521  
Income (loss) from discontinued operations, net of tax (11,605) (1,058) (12,427) (3,421)  
Net income (loss) attributable to Iron Mountain Incorporated $ 67,148 $ 24,345 $ 205,233 $ 161,100  
Weighted-average shares—basic | shares 286,159,000 265,198,000 285,801,000 264,423,000  
Effect of dilutive potential stock options (in shares) | shares 264,451 414,258 250,574 423,688  
Effect of dilutive potential restricted stock, RSUs and PUs (in shares) | shares 558,891 526,725 463,583 446,002  
Weighted-average shares—diluted | shares 286,982,342 266,138,983 286,515,157 265,292,690  
Earnings (Losses) per share-basic:          
Income (Loss) from continuing operations (in dollars per share) | $ / shares $ 0.28 $ 0.10 $ 0.76 $ 0.62  
Total (loss) income discontinued operations (in dollars per share) | $ / shares (0.04) 0.00 (0.04) (0.01)  
Net Income (Loss) Attributable to Iron Mountain Incorporated (in dollars per share) | $ / shares 0.23 0.09 0.72 0.61  
Earnings (Losses) per share-diluted:          
Income (Loss) from continuing operations (in dollars per share) | $ / shares 0.27 0.10 0.76 0.62  
Total (loss) income from discontinued operations (in dollars per share) | $ / shares (0.04) 0.00 (0.04) (0.01)  
Net Income (Loss) Attributable to Iron Mountain Incorporated (in dollars per share) | $ / shares $ 0.23 $ 0.09 $ 0.72 $ 0.61  
Antidilutive stock options, RSUs and PUs, excluded from the calculation (in shares) | shares 3,253,975 2,620,225 3,256,206 2,605,203  
Income Taxes:          
Effective tax rates (as a percent) 15.60% 8.00% 16.20% 15.10%  
Income (Loss) From Continuing Operations Before Income Taxes, Minority Interest, and (Gain) Loss on Disposition of Real Estate $ 91,580 $ 28,288 $ 258,670 $ 195,946  
Federal statutory tax rate (as a percent) 21.00% 35.00% 21.00% 35.00% 35.00%
Tax Matter Resolution, amount released     $ 14,000    
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount   $ 18,457   $ 25,968  
Concentrations of Credit Risk          
Number of global banks with cash, cash equivalent and restricted cash held on deposit | bank 7   7   7
Effective Income Tax Rate Reconciliation Repatriation Of Foreign Earnings, Non-Liquid Assets         8.00%
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Liability         $ 160,000
Income Tax Reconciliation Repatriation Of Foreign Earnings, Attributable To REIT         $ 70,900