Deposit Accounts - The aggregate annual maturities of certificates of deposit accounts (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balance
Within 3 months	$ 479,572
4 to 6 months	365,578
7 to 12 months	264,838
13 to 24 months	179,590
25 to 36 months	43,103
37 to 60 months	13,380
Over 60 months	64,616
Total certificates of deposit accounts	$ 1,410,677	$ 1,084,810
Weighted Average Interest Rate
Within 3 months (as a percent)	1.88%
4 to 6 months (as a percent)	2.03%
7 to 12 months (as a percent)	1.68%
13 to 24 months (as a percent)	1.92%
25 to 36 months (as a percent)	2.01%
37 to 60 months (as a percent)	1.74%
Over 60 months (as a percent)	0.92%
Total certificates of deposit accounts (as a percent)	1.84%	1.10%