Amounts due from parties associated with the reporting entity as evidenced by a written promise to pay, due within 1 year (or 1 business cycle).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_NotesReceivableRelatedPartiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Related Party Transactions (Details) - NSP China - Subsidiaries - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Notes receivable, related parties, current	$ 6,000,000.0		$ 6,000,000.0		$ 6,000,000.0
Company's Joint Venture Partner
Related Party Transaction [Line Items]
Notes receivable, related parties, current	1,500,000		1,500,000		$ 1,500,000
Notes Receivable
Related Party Transaction [Line Items]
Related party transaction, amount	0	$ 2,000,000.0	$ 0	$ 4,000,000.0
Related party transaction, rate			3.00%
Notes Receivable \| Company's Joint Venture Partner
Related Party Transaction [Line Items]
Related party transaction, amount	$ 0	$ 500,000	$ 0	$ 1,000,000.0