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Income Taxes - Operating loss and credit carryforwards (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2017
Federal
Operating loss carryforwards
Operating loss carryforwards expiration year	2027
Illinois
Operating loss carryforwards
Operating loss carryforwards expiration year	2021

X

- Definition

Operating loss carryforwards expiration year.

+ References

No definition available.

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X

- Definition

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.

+ References

No definition available.

+ Details

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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Period Type: