Income Taxes (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Taxes computed at statutory rate, amount	$ 65,423	$ 59,418	$ 84,766
State income taxes, net of federal income tax benefit, amount	1,917	2,595	4,649
Tax-exempt interest, amount	(14,497)	(7,849)	(6,301)
Bank owned life insurance	(4,833)	(3,798)	(3,554)
Tax credits, amount	(10,518)	(12,495)	(16,577)
Other, net, amount	135	433	3,482
Total included in net income	$ 37,627	$ 38,304	$ 66,465
Taxes computed at statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	1.00%	1.50%	1.90%
Tax-exempt interest	(7.80%)	(4.60%)	(2.60%)
Bank owned life insurance	(2.60%)	(2.20%)	(1.50%)
Tax credits	(5.60%)	(7.40%)	(6.80%)
Other, net	0.10%	0.30%	1.40%
Income tax expense	20.10%	22.60%	27.40%
Hancock [Member]
Total included in net income	$ (6,617)	$ (6,334)	$ (3,399)