Investments - Summarized Financial Information (Details) - WMES - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 9,543	$ 7,606
Expenses	8,205	6,904
WMES income before income taxes	1,338	$ 702
Statement of Financial Position [Abstract]
Total assets	325,763		$ 274,744
Total liabilities	238,318		198,534
Total WMES net equity	$ 87,445		$ 76,210