Deposit Accounts - Deposit accounts and weighted average interest rates (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Transaction accounts
Noninterest-bearing checking	$ 3,857,660	$ 3,495,737
Interest-bearing checking	586,019	526,088
Money market	3,171,164	2,975,578
Savings	235,824	250,271
Certificates of deposit accounts
250,000 or less	500,331	569,877
Greater than $250,000	547,511	840,800
Total certificates of deposit accounts	1,047,842	1,410,677
Total deposits	$ 8,898,509	$ 8,658,351
Transaction accounts
Noninterest-bearing checking (as a percent)	0.00%	0.00%
Interest-bearing checking (as a percent)	0.43%	0.38%
Money market (as a percent)	0.83%	0.89%
Savings (as a percent)	0.16%	0.14%
Certificates of deposit accounts
Less than $100,000 (as a percent)	1.59%	1.44%
Greater than $250,000 (as a percent)	1.77%	2.12%
Total certificates of deposit accounts (as a percent)	1.69%	1.84%
Total deposits (as a percent)	0.53%	0.63%