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Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transactions
Receivable from related party	$ 149		$ 149		$ 169
USAA
Related Party Transactions
Receivable from related party	100		100		200
Due to Related Parties	4,600		4,600		$ 3,300
USAA \| Sales and marketing
Related Party Transactions
Costs under related party agreements	$ 5,300	$ 4,500	$ 9,800	$ 8,500