Deposits - Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deposits
Non-interest bearing checking	$ 3,921,710	$ 3,671,915
Interest bearing checking	2,459,617	2,628,212
Total checking	6,381,327	6,300,127
Savings	6,122,257	5,287,606
Money market	1,609,422	1,764,998
Certificates of deposit	4,790,680	4,982,271
Total deposits	$ 18,903,686	$ 18,335,002
Year-to-Date Weighted-average Rate
Interest bearing checking	0.03%	0.01%
Total checking	0.01%	0.01%
Savings	0.36%	0.09%
Money market	0.75%	0.47%
Certificates of deposit	1.53%	1.14%
Total deposits	0.58%	0.38%