Employee Stock Benefit Plans - Restricted Stock Units - General Information (Details) - Restricted stock units	6 Months Ended
Jun. 30, 2018 shares
Stock Benefit Plans
Right to number of shares of common stock per RSU (in shares)	1
Vesting percentage (as a percent)	25.00%

Percentage of vesting of share-based compensation awards.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration