Fair Value - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value [Line Items]
Total amount of loans being serviced for the benefit of others at the end of the year	$ 607,016	$ 640,530	$ 242,915
Minimum
Fair Value [Line Items]
Appraisal adjustment (percent)	0.00%
Maximum
Fair Value [Line Items]
Appraisal adjustment (percent)	15.00%