This is the closest type insurance to
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excess property insurance

Insurance protection for large property risks that provides a layer of coverage above the primary layer. The primary policy will cover most property losses while the excess layer of coverage does not respond until the primary layer has exhausted all applicable limits. The primary layer acts much the same as a very large deductible.
https://www.dadgarinsurance.com/ins_words/eee/e054.htm

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Excess insurance – Coverage that applies on top of underlying insurance that is primary, i.e., that pays until its coverage limit is exhausted at which point that excess coverage takes over.
https://dentistsbenefits.com/resources/glossary-insurance-te...

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CFSA purchases excess property insurance policies that provide a $100 million protection limit excess of the first $500,000 protection of the pool.

http://www.cfsa.org/cgi/selfinsure/selfinsure.htm

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When additional protection is needed beyond the underlying primary property policy, we can offer excess coverage that can be tailored to meet your specific needs featuring:

Excess capacity of $1,000,000 or greater
Large and complicated risks
Innovative Risk Control services
Responsive Claim services
Ability to round out property programs with solutions including equipment breakdown, inland, and crime.
https://www.travelers.com/business-insurance/large/excess-pr...

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Note added at 1 hr (2017-10-14 18:56:42 GMT)
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coverage can be understood as amount as well, so that it is sufficient to say
excess property insurance coverage