Investment Securities (Contractual Maturities Debt Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investments [Abstract]
Held-to-maturity, Due in one year or less, Amortized cost	$ 77,395
Held-to-maturity, Due in one year or less, Estimated fair value	56,283
Held-to-maturity, Due after one year through five years, Amortized cost	195,088
Held-to-maturity, Due after one year through five years, Estimated fair value	161,077
Held-to-maturity, Due after five years through ten years, Amortized cost	135,308
Held-to-maturity, Due after five years through ten years, Estimated fair value	138,806
Held-to-maturity, Due after ten years, Amortized cost	239,595
Held-to-maturity, Due after ten years, Estimated fair value	279,213
Held-to-maturity, Amortized cost	647,386	630,574
Held-to-maturity, fair value	635,379	609,547
Available-for-sale, Due in one year or less, Amortized cost	510,870
Available-for-sale, Due in one year or less, Estimated fair value	497,041
Available-for-sale, Due after one year through five years, Amortized cost	1,212,400
Available-for-sale, Due after one year through five years, Estimated fair value	1,205,205
Available-for-sale, Due after five years through ten years, Amortized cost	709,151
Available-for-sale, Due after five years through ten years, Estimated fair value	697,454
Available-for-sale, Due after ten years, Amortized cost	891,226
Available-for-sale, Due after ten years, Estimated fair value	771,443
Available-for-sale, Amortized cost	3,323,647
Available-for-sale, Estimated fair value	$ 3,171,143	$ 3,421,683