Concentration of Credit Risk - Additional Information (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Concentration Risk [Line Items]
Deposit amount exceeding the FDIC insurance limit	$ 2.2
First American Retail Prime Obligation Money Market Fund [Member]
Concentration Risk [Line Items]
Uninsured amount of cash and cash equivalents	$ 22.9

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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