Deposits - Categorized by Interest-bearing or Noninterest-bearing (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
U.S.:
Interest-bearing	$ 10,800,140	$ 10,129,958
Noninterest-bearing	5,494,803	5,399,212
Foreign:
Interest-bearing	685,129	671,957
Noninterest-bearing	632,050	593,405
Total deposits	$ 17,612,122	$ 16,794,532