Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Available-for-Sale, Amortized Cost
Due within one year		$ 130,166
Due after one year through five years		449,624
Due after five years through ten years		137,566
Due after ten years		708,846
Total before residential mortgage-backed securities		1,426,202
Total		2,336,693	$ 2,341,767
Available-for-Sale, Fair Value
Due within one year		130,744
Due after one year through five years		451,570
Due after five years through ten years		139,651
Due after ten years		724,194
Total before residential mortgage-backed securities		1,446,159
Total		2,361,830	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		5,462
Due after ten years		587,852
Total before residential mortgage-backed securities		593,314
Amortized Cost		593,314	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		5,384
Due after ten years		603,397
Total before residential mortgage-backed securities		608,781
Total		608,781	550,946
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	[1]	910,491
Total		910,491	1,043,897
Available-for-Sale, Fair Value
Residential mortgage-backed securities	[1]	915,671
Total		915,671	$ 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.