Investments (Maturity Information) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment securities available for sale
Total investment securities available for sale, cost	$ 5,680,970	$ 5,404,335
Total investment securities available for sale, fair value	5,676,237	5,387,703
Investment securities held to maturity
Investment securities held to maturity	782	907
Debt Securities
Investment securities available for sale
Maturing in one year or less, cost	829,091	839,956
Maturing in one through five years, cost	2,258,570	2,077,539
Maturing in one year or less, fair value	829,997	840,883
Maturing in one through five years, fair value	2,257,014	2,077,800
Equity Securities
Investment securities available for sale
Total investment securities available for sale, cost	543	543
Total investment securities available for sale, fair value	22,560	22,147
Mortgage Backed Securities, Other [Member]
Investment securities available for sale
Total investment securities available for sale, cost	2,592,766	2,486,297
Total investment securities available for sale, fair value	2,566,666	2,446,873
Investment securities held to maturity
Investment securities held to maturity	782	907
Fair Value	$ 835	$ 974