Investment Securities Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Available-for-Sale, Amortized Cost
Due within one year		$ 140,703
Due after one year through five years		486,235
Due after five years through ten years		128,158
Due after ten years		629,369
Total before residential mortgage-backed securities		1,384,465
Total		2,588,013	$ 2,341,767
Available-for-Sale, Fair Value
Due with one year		141,230
Due after one year through five years		484,467
Due after five years through ten years		131,883
Due after ten years		652,220
Total before residential mortgage-backed securities		1,409,800
Total		2,610,760	2,387,428
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		0
Due after five years through ten years		25,073
Due after ten years		676,999
Total before residential mortgage-backed securities		702,072
Amortized Cost		702,072	520,997
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		25,605
Due after ten years		703,908
Total before residential mortgage-backed securities		729,513
Total		729,513	550,946
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	[1]	1,203,548
Total		1,203,548	1,043,897
Available-for-Sale, Fair Value
Residential mortgage-backed securities	[1]	1,200,960
Total		1,200,960	$ 1,052,616
Held-to-Maturity, Amortized Cost
Residential mortgage-backed securities	[1]	0
Held-to-Maturity, Fair Value
Residential mortgage-backed securities	[1]	$ 0

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