Summary of Significant Accounting Policies - Adoption of New Accounting Standards (Details)	12 Months Ended
Dec. 31, 2017 USD ($)
Accounting Standards Update 2016-09 [Member]
Reduction to income tax expenses	$ 146,000
ASU 2018-02
Reclassification resulting from the Tax Act	1,019,000
Adjustments \| Accounting Standards Update 2016-09 [Member]
Reduction to income tax expenses	$ 146,000

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=SL79508275-113901

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration