Quarterly report pursuant to Section 13 or 15(d)

Related Party Transactions (Details)

v3.19.2
Related Party Transactions (Details) - NSP China - Subsidiaries - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Related Party Transaction [Line Items]          
Notes receivable, related parties, current $ 6,200,000   $ 6,200,000   $ 6,000,000
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 $ 0 $ 0 $ 2,000,000  
Related party transaction, rate     3.00%    
Notes Receivable | Company's Joint Venture Partner          
Related Party Transaction [Line Items]          
Related party transaction, amount $ 0 $ 0 $ 0 $ 500,000