Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Available-for-Sale, Amortized Cost
Due within one year		$ 142,316
Due after one year through five years		467,688
Due after five years through ten years		176,826
Due after ten years		595,641
Total before residential mortgage-backed securities		1,382,471
Total		2,424,592	$ 2,588,013
Available-for-Sale, Fair Value
Due within one year		142,834
Due after one year through five years		472,160
Due after five years through ten years		187,546
Due after ten years		627,627
Total before residential mortgage-backed securities		1,430,167
Total		2,487,955	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		39,376
Due after ten years		641,198
Total before residential mortgage-backed securities		680,574
Amortized Cost		680,574	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		41,965
Due after ten years		684,400
Total before residential mortgage-backed securities		726,365
Total		726,365	729,513
Residential mortgage-backed securities
Available-for-Sale, Amortized Cost
Residential mortgage-backed securities	[1]	1,042,121
Total		1,042,121	1,203,548
Available-for-Sale, Fair Value
Residential mortgage-backed securities	[1]	1,057,788
Total		1,057,788	$ 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.