Securities Available for Sale and Held to Maturity - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Dec. 31, 2013
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Reclassification of Securities available for sale to securities held to maturity			$ 1,099,000,000.000
Net unrealized holding loss on AFS Securities at date of transfer			46,600,000
Net unrealized holding losses on AFS Securities, net of tax at date of transfer			$ 28,800,000
Net unamortized, unrealized loss on transfer of securities	$ 7,500,000	$ 8,900,000
Net unamortized, unrealized loss on transfer of securities, net of tax	5,600,000	6,700,000
Credit loss recognized	0	0
Potential credit loss exposure	13,000,000.0	26,600,000
Pledged to collateralize public deposits and securities sold under repurchase agreements and for other purposes as permitted by law	2,163,000,000	1,964,000,000
Pledged securities providing additional contingency funding	0	0
30 Days or More Past Due [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Held-to-maturity, past due	0	0
Securities Available for Sale [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Accrued interest receivable	4,200,000	4,000,000.0
Securities Held to Maturity [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Accrued interest receivable	888,000	1,200,000
Reserve for credit loss	0	0
Held-to-maturity nonnaccrual	$ 0	$ 0