Loans and Allowance for Credit Losses - Summary of Changes in Accretable Discount for ACI Loans (Details) - ACI Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Balance at beginning of period	$ 78,422	$ 98,728	$ 122,791
Maturities/payoff	(7,456)	(9,888)	(11,563)
Charge-offs	(77)	(129)	(286)
Foreclosure	(436)	(1,061)	(1,041)
Accretion	(19,813)	(23,303)	(30,870)
Reclass from nonaccretable difference due to increases in expected cash flow	16,765	14,075	19,697
Balance at end of period	$ 67,405	$ 78,422	$ 98,728