Summary of Significant Accounting Policies - Fair Value of Financial Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 29,632	$ 10,380	$ 7,808	$ 11,012
Restricted cash	1,212	693	1,058	1,078
Restricted cash for Development Projects	33,799	41,982	$ 7,605	$ 26,384
Short-term Investments	33,400	94,500
Long-term Debt	482,513	469,736
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	29,632	10,380
Cash and Cash Equivalents, Fair Value Disclosure	29,632	10,380
Restricted cash	1,212	693
Restricted Cash, Current, Fair Value Disclosure	1,212	693
Restricted cash for Development Projects	33,799	41,982
Restricted Cash, Noncurrent, Fair Value Disclosure	33,799	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	33,400	94,449
Short-term Investments, Fair Value Disclosure	33,155	94,209
Bangkok Bank 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]
Lines of Credit, Fair Value Disclosure	16,000	16,000
Long-term Line of Credit	16,000	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	13	0
Long-term Line of Credit	13,000	0
Equipment Loans [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	30,731	31,095
Lines of Credit, Fair Value Disclosure	31	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	222	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	443,322	443,161
Notes Payable, Fair Value Disclosure	449,778	449,749
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments	26,400	59,400
US Treasury Notes Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments	$ 7,000	$ 35,100