Investment Securities Taxable and Nontaxable Interest Income by Investment Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Noninterest Income	$ 28,809	$ 24,502	$ 56,282	$ 52,596
Taxable [Member]
Noninterest Income	25,340	21,067	49,298	45,801
Nontaxable [Member]
Noninterest Income	3,469	3,435	6,984	6,795
Held-to-maturity Securities [Member]
Noninterest Income	5,867	6,528	12,321	13,192
Held-to-maturity Securities [Member] | Taxable [Member]
Noninterest Income	3,093	3,721	6,685	7,549
Held-to-maturity Securities [Member] | Nontaxable [Member]
Noninterest Income	2,774	2,807	5,636	5,643
Available-for-sale Securities [Member]
Noninterest Income	22,332	17,408	42,753	38,356
Available-for-sale Securities [Member] | Taxable [Member]
Noninterest Income	21,637	16,780	41,405	37,204
Available-for-sale Securities [Member] | Nontaxable [Member]
Noninterest Income	695	628	1,348	1,152
Trading Securities [Member]
Noninterest Income	610	566	1,208	1,048
Trading Securities [Member] | Taxable [Member]
Noninterest Income	610	566	1,208	1,048
Trading Securities [Member] | Nontaxable [Member]
Noninterest Income	$ 0	$ 0	$ 0	$ 0