Stock-based Compensation and Other Employee Benefits - Valuation Assumptions for Stock Options and ESPP Purchase - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options granted (in shares)	0

Gross number of share options (or share units) granted during the period.

No definition available.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration