Operating Expenses - Components of Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Income and Expenses [Abstract]
Fixed compensation expense	$ 9,391	$ 5,922	$ 26,848	$ 18,136
Variable compensation expense	4,090	4,923	12,513	13,655
Equity compensation expense	3,155	3,033	10,132	9,565
Total compensation expense	16,636	13,878	49,493	41,356
Systems and consulting	3,230	1,794	7,594	5,434
Loan acquisition costs	1,392	1,887	4,385	5,860
Office costs	1,517	1,173	4,406	3,397
Accounting and legal	1,767	1,170	3,852	3,078
Corporate costs	482	462	1,701	1,462
Other operating expenses	1,791	1,126	4,798	2,942
Total Operating Expenses	$ 26,815	$ 21,490	$ 76,229	$ 63,529