Summary of Significant Accounting Policies - Additional Information (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Non-controlling interest	$ 0	$ 361
Cash equivalents maximum maturity period of highly liquid investments	90 days
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of business days for related transactions	1 day
Loan forgiven over service period	3 years
Minimum [Member] | Furniture and Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Depreciation and amortization on straight-line basis	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of business days for related transactions	2 days
Loan forgiven over service period	9 years
Maximum [Member] | Furniture and Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Depreciation and amortization on straight-line basis	7 years
Securities
Summary Of Significant Accounting Policies [Line Items]
Number of business days for related transactions	2 days
Commodities
Summary Of Significant Accounting Policies [Line Items]
Number of business days for related transactions	1 day