Stockholders' Equity - Additional Information (Detail) - At the Market Equity Distribution Agreement $ in Thousands		3 Months Ended
May 06, 2016 USD ($) sales_agent	Mar. 31, 2019 USD ($) shares
Class of Stock [Line Items]
Aggregate offering price of common shares	$ 400,000
Number of sales agents \| sales_agent	5
Shares, issued (in shares) \| shares		0
Value of stock available for issuance under ATM		$ 257,929

Number of new stock issued during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration