Derivative Financial Instruments - Summary of Derivative Positions (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivatives contracts	$ 602,682	$ 604,118
Forward rate commitments
Derivative [Line Items]
Derivatives contracts	430,389	429,283
Interest rate lock commitments
Derivative [Line Items]
Derivatives contracts	$ 172,293	$ 174,835