Interest Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Banking and Thrift, Interest [Abstract]
Interest on unpaid principal balance	$ 382,983	$ 300,713	$ 227,579
Interest on deposits	132	171	408
Amortization of net deferred origination costs	(48,540)	(36,040)	(32,939)
Total interest income	$ 334,575	$ 264,844	$ 195,048