Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Available-for-Sale, Amortized Cost
Due within one year		$ 150,150
Due after one year through five years		503,233
Due after five years through ten years		144,750
Due after ten years		629,795
Total before residential mortgage-backed securities		1,427,928
Total		2,568,341	$ 2,588,013
Available-for-Sale, Fair Value
Due within one year		150,764
Due after one year through five years		503,879
Due after five years through ten years		149,613
Due after ten years		654,212
Total before residential mortgage-backed securities		1,458,468
Total		2,604,625	2,610,760
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		28,545
Due after ten years		663,118
Total before residential mortgage-backed securities		691,663
Amortized Cost		691,663	702,072
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		29,370
Due after ten years		690,820
Total before residential mortgage-backed securities		720,190
Total		720,190	729,513
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	[1]	1,140,413
Total		1,140,413	1,203,548
Available-for-Sale, Fair Value
Residential mortgage-backed securities	[1]	1,146,157
Total		1,146,157	$ 1,200,960
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.