UNHCR: Detention Guidelines 2012

Detention Guidelines: guidelines on the applicable criteria and standards relating to the detention of asylum-seekers and alternatives to detention: http://www.unhcr.org/refworld/pdfid/503489533b8.pdf

Indefinite detention is arbitrary and maximum limits on detention should be established in law

44. As indicated in Guideline 4.2, the test of proportionality applies in relation to both the initial order of detention as well as any extensions. The length of detention can render an otherwise lawful decision to detain disproportionate and, therefore, arbitrary. Indefinite detention for immigration purposes is arbitrary as a matter of international human rights law.
45. Asylum-seekers should not be held in detention for any longer than necessary; and where the justification is no longer valid, the asylum-seeker should be released immediately (Guideline 4.1).

46. To guard against arbitrariness, maximum periods of detention should be set in national legislation. Without maximum periods, detention can become prolonged, and in some cases indefinite, including particularly for stateless asylum-seekers. Maximum periods in detention cannot be circumvented by ordering the release of an asylum-seeker only to re-detain them on the same grounds shortly afterwards.