Deposits Deposits (Summary of Deposits) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Balance:
Non-interest bearing	$ 4,705,994	$ 3,518,685	$ 3,253,477
NOW and interest bearing demand deposits	2,231,258	2,236,089	2,086,099
Wealth management deposits	1,469,920	1,226,916	1,212,317
Money market	4,001,518	3,651,467	3,744,682
Savings	1,684,007	1,508,877	1,465,250
Time certificates of deposit	4,135,772	4,139,810	4,303,421
Total deposits	$ 18,228,469	$ 16,281,844	$ 16,065,246
Mix:
Non-interest bearing	26.00%	22.00%	20.00%
NOW and interest bearing demand deposits	12.00%	14.00%	13.00%
Wealth management deposits	8.00%	8.00%	8.00%
Money market	22.00%	22.00%	23.00%
Savings	9.00%	9.00%	9.00%
Time certificates of deposit	23.00%	25.00%	27.00%
Total deposits	100.00%	100.00%	100.00%