Deposits (Summary of Average Balances and Weighted Average Rates Paid on Deposits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Demand deposits:
Non-interest bearing, average balance	$ 3,389,191	$ 3,069,565	$ 2,968,192
Non-interest bearing, average rate (in Percent)	0.00%	0.00%	0.00%
Interest bearing, average balance	$ 1,627,828	$ 1,586,390	$ 1,382,717
Interest-bearing, average rate (in Percent)	1.13%	0.81%	0.60%
Money market, average balance	$ 10,350,772	$ 9,364,498	$ 7,946,447
Weighted Average Rate Domestic Deposit, Money Market	1.41%	0.85%	0.64%
Savings, average balance	$ 284,198	$ 365,603	$ 415,205
Weighted Average Rate Domestic Deposit, Savings	0.26%	0.21%	0.23%
Time, average balance	$ 6,617,006	$ 6,094,336	$ 5,326,630
Weighted Average Rate Domestic Deposit, Time Deposits	1.81%	1.27%	1.12%
Total, average balance	$ 22,268,995	$ 20,480,392	$ 18,039,191
Weighted Average Rate, Interest-bearing Domestic Deposits, Point in Time	1.28%	0.83%	0.66%