Investment Securities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 01, 2019
Gain (Loss) on Securities [Line Items]
Trading securities	$ 0
Weighted average duration of MBS portfolio	2 years 8 months 12 days
Securities pledged as collateral	$ 1,300,000,000	$ 1,100,000,000
Sale of investment securities available-for-sale	305,812,000	618,194,000	$ 7,012,000
Proceeds from sale of debt securities	9,100,000	39,800,000
Losses from sale of available-for-sale securities (less than during the current quarter end)	0	0	0
Gain on sale of investment securities available for sale		300,000	$ 100,000
Unamortized premiums	60,400,000	15,100,000
Unaccreted discounts	2,600,000	$ 4,100,000
Owned investment securities	583,900,000
Total unrealized losses on securities	2,100,000
Held-to-maturity debt securities with an amortized cost basis	111,700,000
Accrued interest	$ 1,100,000
Beneficial
Gain (Loss) on Securities [Line Items]
Securities sold				$ 578,800,000