Investment Securities Maturity Schedule (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Available-for-Sale, Amortized Cost
Due within one year	$ 110,456
Due after one year through five years	510,168
Due after five years through ten years	61,297
Due after ten years	662,166
Total, single maturity date	1,344,087
Total	2,640,616
Available-for-Sale, Fair Value
Due within one year	111,108
Due after one year through five years	516,571
Due after five years through ten years	61,933
Due after ten years	677,465
Total, single maturity date	1,367,077
Total	2,669,180
Held-to-Maturity, Carrying Value
Due within one year	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	481,476
Total, single maturity date	481,476
Total	481,476		0
Held-to-Maturity, Fair Value
Due within one year	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	498,902
Total, single maturity date	498,902
Total	498,902		0
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	1,296,529	[1]
Available-for-Sale, Fair Value
Residential mortgage-backed securities	1,302,103	[1]
Held-to-Maturity, Carrying Value
Residential mortgage-backed securities	0	[1]
Held-to-Maturity, Fair Value
Residential mortgage-backed securities	$ 0	[1]

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