Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Available-for-Sale, Amortized Cost
Due within one year		$ 155,812
Due after one year through five years		432,211
Due after five years through ten years		151,861
Due after ten years		672,491
Total before residential mortgage-backed securities		1,412,375
Total		2,494,301	$ 2,341,767
Available-for-Sale, Fair Value
Due within one year		156,630
Due after one year through five years		433,896
Due after five years through ten years		156,083
Due after ten years		693,308
Total before residential mortgage-backed securities		1,439,917
Total		2,530,994	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		18,557
Due after ten years		633,265
Total before residential mortgage-backed securities		651,822
Amortized Cost		651,822	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		18,706
Due after ten years		653,689
Total before residential mortgage-backed securities		672,395
Total		672,395	550,946
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	[1]	1,081,926
Total		1,081,926	1,043,897
Available-for-Sale, Fair Value
Residential mortgage-backed securities	[1]	1,091,077
Total		1,091,077	$ 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.