Maturities of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Available-for-Sale Amortized Cost, Within One Year	$ 261,829
Available-for-Sale Amortized Cost, After One Year but Within Five Years	1,074,666
Available-for-Sale Amortized Cost, After Five Years but Within Ten Years	181,258
Available-for-Sale Amortized Cost, After Ten Years	66,850
Available-for-Sale, Amortized Cost	1,584,603	1,971,757
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Available-for-Sale Estimated Fair Value, Within One Year	263,597
Available-for-Sale Estimated Fair Value, After One Year but Within Five Years	1,075,712
Available-for-Sale Estimated Fair Value, After Ten Years	179,828
Available-for-Sale Estimated Fair Value, After Five Years but Within Ten Years	67,366
Available-for-Sale, Estimated Fair Value	1,586,503	1,947,706
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount
Held-to-Maturity Amortized Cost, Within One Year	88,305
Held-to-Maturity Amortized Cost, After One Year but Within Five Years	285,622
Held-to-Maturity Amortized Cost, After Five Years but Within Ten Years	144,409
Held-to-Maturity Amortized Cost, After Ten Years	64,935
Held-to-Maturity, Amortized Cost	583,271	203,837
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity
Held-to-Maturity Estimated Fair Value, Within One Year	88,490
Held-to-Maturity Estimated Fair Value, After One Year but Within Five Years	286,860
Held-to-Maturity Estimated Fair Value, After Five Years but Within Ten Years	146,353
Held-to-Maturity Estimated Fair Value, After Ten Years	66,329
Held-to-Maturity, Estimated Fair Value	588,032	205,926
Callable Within One Year
Available-for-sale Securities and Held-to-maturity Securities
Investment Securities Primarily Classified as Available-for-Sale, Amortized Costs, After One Year but Within Five Years	178,937
Investment Securities Primarily Classified as Available-for-Sale, Fair Value, After One Year but Within Five Years	178,814
Callable Structured Notes
Available-for-sale Securities and Held-to-maturity Securities
Investment Securities Primarily Classified as Available-for-Sale, Amortized Costs, After One Year but Within Five Years	69,967
Investment Securities Primarily Classified as Available-for-Sale, Fair Value, After One Year but Within Five Years	$ 69,997