Deposits (Summary of Deposits) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Balance:
Non-interest bearing	$ 6,612,319	$ 6,792,497	$ 5,790,579
NOW and interest bearing demand deposits	2,315,122	2,315,055	2,484,676
Wealth management deposits	2,495,134	2,323,699	2,390,464
Money market	4,617,122	4,515,353	4,555,752
Savings	2,901,504	2,829,373	2,287,958
Time certificates of deposit	4,338,126	4,407,370	4,221,012
Total deposits	$ 23,279,327	$ 23,183,347	$ 21,730,441
Mix:
Non-interest bearing	28.00%	29.00%	27.00%
NOW and interest bearing demand deposits	10.00%	10.00%	11.00%
Wealth management deposits	11.00%	10.00%	11.00%
Money market	20.00%	20.00%	21.00%
Savings	12.00%	12.00%	11.00%
Time certificates of deposit	19.00%	19.00%	19.00%
Total deposits	100.00%	100.00%	100.00%