Investment Securities Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Available-for-Sale, Amortized Cost
Due within one year		$ 149,379
Due after one year through five years		437,896
Due after five years through ten years		197,462
Due after ten years		521,338
Total before mortgage-backed securities		1,306,075
Total		2,422,802	$ 2,588,013
Available-for-Sale, Fair Value
Due with one year		149,650
Due after one year through five years		438,650
Due after five years through ten years		200,654
Due after ten years		528,347
Total before mortgage-backed securities		1,317,301
Total		2,425,477	2,610,760
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		594
Due after five years through ten years		55,310
Due after ten years		619,770
Total before mortgage-backed securities		675,674
Amortized Cost		675,674	702,072
Held-to-Maturity, Fair Value
Due within one year		0
Due after one year through five years		597
Due after five years through ten years		56,048
Due after ten years		632,444
Total before mortgage-backed securities		689,089
Total		689,089	729,513
Mortgage-backed securities
Available-for-Sale, Amortized Cost
Mortgage-backed securities	[1]	1,116,727
Total		1,116,727	1,203,548
Available-for-Sale, Fair Value
Mortgage-backed securities	[1]	1,108,176
Total	[2]	1,108,176	$ 1,200,960
Held-to-Maturity, Amortized Cost
Mortgage-backed securities	[1]	0
Held-to-Maturity, Fair Value
Mortgage-backed securities	[1]	$ 0

[1] Mortgage-backed securities, which have prepayment provisions, are not assigned to maturity categories due to fluctuations in their prepayment speeds.

[2] Consists of residential mortgage-backed securities with fair values of $1,011,252,000 and $1,200,503,000 at December 31, 2016 and 2015, respectively, and commercial mortgage-backed securities, with fair values of $96,924,000 and $457,000 at December 31, 2016 and 2015, respectively.