Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 1,640,299	$ 1,408,780
Held to maturity securities	2,253,219	2,576,584
Property and equipment, accumulated depreciation	$ 187,692	$ 172,798
Common stock, par value per share	$ 3.33	$ 3.33
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares outstanding	81,566,640	82,237,162