Nature of Business - Revenue Recognition - Practical Expedients (Details)	6 Months Ended
Jun. 30, 2018
Practical expedients
Practical Expedient, Incremental Cost	true
Practical Expedient, Use of Transaction Price	true
Practical Expedient, Nonrestatement of Modified Contract	true

No definition available.

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether practical expedient was elected to recognize incremental cost of obtaining contract as expense when incurred if amortization period would have been one year or less.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130569-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL51790836-203054

+ Details

Name:	us-gaap_RevenuePracticalExpedientIncrementalCostOfObtainingContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether practical expedient was elected under initial application of retrospective method to use transaction price at date when contract with variable consideration was completed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=113356391&loc=SL49131195-203048

+ Details

Name:	us-gaap_RevenuePracticalExpedientInitialApplicationAndTransitionCompletedContractUseOfTransactionPriceAtContractCompletionDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether practical expedient was elected under initial application of retrospective method to aggregate effect of contract modified before beginning of earliest period presented when identifying satisfied and unsatisfied performance obligation, determining transaction price and allocating transaction price to performance obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (f)(4)
-URI http://asc.fasb.org/extlink&oid=113356391&loc=SL49131195-203048

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration