Net Loss Per Share - Additional Information (Detail)	Dec. 31, 2018 $ / shares
1.75% Convertible Senior Notes due 2021 [Member]
Earnings Per Share Diluted [Line Items]
Convertible notes, conversion price	$ 96.37

The price per share of the conversion feature embedded in the debt instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031898-161870

Name:	us-gaap_DebtInstrumentConvertibleConversionPrice1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant