Summary of Significant Accounting Policies - Fair Value of Financial Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 18,390	$ 10,380	$ 6,213	$ 11,012
Restricted cash	502	693	920	1,078
Restricted cash for Development Projects		41,982	$ 45,212	$ 26,384
Restricted cash for Development Projects		42,000
Short-term Investments		94,500
Long-term Debt	546,763	469,736
Long-term loan, related party, net of debt issuance costs	20,064	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value		10,380
Cash and Cash Equivalents, Fair Value Disclosure	18,390	10,380
Restricted cash	502
Restricted cash		693
Restricted Cash, Current, Fair Value Disclosure	502	693
Restricted cash for Development Projects	64,178
Restricted cash for Development Projects		41,982
Restricted Cash, Noncurrent, Fair Value Disclosure	64,178	41,982
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments	0	94,449
Short-term Investments, Fair Value Disclosure	0	94,209
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Payable, Fair Value Disclosure	20,064	0
Long-term loan, related party, net of debt issuance costs	20,064
Notes Payable, Related Parties		0
Term Loan Facility, Term B Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash for Development Projects	64,200
Bangkok Bank Loan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure	18,000	16,000
Long-term Line of Credit	18,000	16,000
Fifth Third Revolver [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure	15	0
Long-term Line of Credit	15,000	0
Equipment Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	24,100
Equipment Loans [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	24,057	31,095
Lines of Credit, Fair Value Disclosure	24,057	31,095
Interest Rate Cap [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	287	251
Notes Payable to Banks [Member] | Term Loan Facility, Term B Loan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	441,635	443,161
Notes Payable, Fair Value Disclosure	447,463	449,749
Notes Payable to Banks [Member] | Term Loan Facility, Term A Loan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	66,500	0
Notes Payable, Fair Value Disclosure	$ 66,500	0
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments		59,400
US Treasury Notes Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments		$ 35,100