Fair Value of Financial Instruments - Summary of Aggregate Fair Value and Unpaid Principal Balance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair value of gain (loss) related to mortgage banking activities	$ 4,200	$ (2,800)	$ 464
Difference between the aggregate fair value and the aggregate unpaid principal balance
Loans held-for-sale, aggregate fair value	269,140	252,712
Loans held-for-sale, aggregate unpaid principal balance under FVO	262,315	250,095
Loans held-for-sale, fair value over/(under) unpaid principal	$ 6,825	$ 2,616