Investment Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Trading securities	$ 0
Securities pledged as collateral	1,100,000,000	$ 914,500,000
Proceeds from sale of debt securities	39,800,000
Sale of investment securities available for sale	618,194,000	7,012,000	$ 457,046,000
Gain on sale of investment securities available for sale	300,000	100,000	2,100,000
Losses from sale of available-for-sale securities (less than during the current quarter end)	0	0	100,000
Proceeds from sale of equity securities	0	6,200,000	0
Realized gain on sale of equity investment	0	3,757,000	$ 0
Realized losses on equity securities		0
Unamortized premiums	15,100,000	12,700,000
Unaccreted discounts	4,100,000	2,500,000
Owned investment securities	418,500,000
Total unrealized losses on securities	$ 4,000,000.0
Number of securities, below investment grade | security	1
Fair value	$ 400,000
OTTI	$ 0	$ 0
Weighted average duration of MBS portfolio	3 years 8 months 12 days