Number of new stock issued during the period.

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-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended
	Apr. 30, 2018	Mar. 31, 2019	May 31, 2017	Dec. 07, 2016
ATM Agreement [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock issuable and sellable under offering agreement		$ 75.0	$ 75.0	$ 75.0
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares issued	14.2
Public offering price of common stock issued	$ 16.25
Net proceeds from issuance of common stock, after deducting offering expenses	$ 215.8