Investments - Summarized Financial Information (Details) - WMES - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 13,007	$ 9,987	$ 36,144	$ 26,633
Expenses	9,657	8,408	27,378	22,762
WMES income before income taxes	3,350	$ 1,579	8,766	$ 3,871
Statement of Financial Position [Abstract]
Total assets	313,073		313,073		$ 274,744
Total liabilities	225,727		225,727		198,534
Total WMES net equity	$ 87,346		$ 87,346		$ 76,210