Fair Value Measurements - Narrative (Details)	Mar. 31, 2018
Level 1
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Investment portfolio percentage	5.20%
Level 2
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Investment portfolio percentage	92.00%

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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