Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Short term investments	$ 0.0	$ 0.7
Clinton Group
Debt Securities, Available-for-sale [Line Items]
Short term investments	$ 0.0	$ 0.4

Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 942
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-Section S99
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant