Deposit Accounts - Deposit Accounts and Weighted Average Interest Rates (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Transaction accounts
Noninterest-bearing checking	$ 6,011,106	$ 3,857,660
Interest-bearing checking	2,913,260	586,019
Money market	5,302,073	3,171,164
Savings	360,896	235,824
Certificates of deposit accounts
$250,000 or less	800,957	500,331
Greater than $250,000	825,885	547,511
Total certificates of deposit accounts	1,626,842	1,047,842
Total deposits	$ 16,214,177	$ 8,898,509
Transaction accounts
Noninterest-bearing checking (as a percent)	0.00%	0.00%
Interest-bearing checking (as a percent)	0.06%	0.43%
Money market (as a percent)	0.23%	0.83%
Savings (as a percent)	0.09%	0.16%
Certificates of deposit accounts
Less than $100,000 (as a percent)	0.88%	1.59%
Greater than $250,000 (as a percent)	0.88%	1.77%
Total	0.88%	1.69%
Total deposits (as a percent)	0.18%	0.53%