Revenues - Impact of Adoption of Topic 606 (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Prepaid expenses and other assets	$ 29,444	$ 25,011
Liabilities and stockholders' equity
Unearned income	33,682
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Prepaid expenses and other assets	29,560
Liabilities and stockholders' equity
Unearned income	34,572
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
Assets
Prepaid expenses and other assets	116
Liabilities and stockholders' equity
Unearned income	$ 890

Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(8))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(7))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

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Balance Type:	debit
Period Type:	instant