Investment Securities Investment Securities (Tax and Nontaxable Income by Investment Type) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Interest on securities	$ 203,920	$ 124,086	$ 101,936
Trading Securities [Member]
Investment [Line Items]
Interest on securities	3,123	2,214	1,979
Available-for-sale Securities [Member]
Investment [Line Items]
Interest on securities	177,863	98,203	73,923
Held-to-maturity Securities [Member]
Investment [Line Items]
Interest on securities	22,934	23,669	26,034
Taxable [Member]
Investment [Line Items]
Interest on securities	179,710	109,868	88,114
Taxable [Member] | Trading Securities [Member]
Investment [Line Items]
Interest on securities	3,123	2,214	1,979
Taxable [Member] | Available-for-sale Securities [Member]
Investment [Line Items]
Interest on securities	166,281	94,877	71,365
Taxable [Member] | Held-to-maturity Securities [Member]
Investment [Line Items]
Interest on securities	10,306	12,777	14,770
Nontaxable [Member]
Investment [Line Items]
Interest on securities	24,210	14,218	13,822
Nontaxable [Member] | Trading Securities [Member]
Investment [Line Items]
Interest on securities	0	0	0
Nontaxable [Member] | Available-for-sale Securities [Member]
Investment [Line Items]
Interest on securities	11,582	3,326	2,558
Nontaxable [Member] | Held-to-maturity Securities [Member]
Investment [Line Items]
Interest on securities	$ 12,628	$ 10,892	$ 11,264