Investment Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Available-for-Sale, Amortized Cost
Due within one year		$ 173,687
Due after one year through five years		344,407
Due after five years through ten years		219,792
Due after ten years		385,173
Total before mortgage-backed securities		1,123,059
Total		2,119,194	$ 2,422,802
Available-for-Sale, Fair Value
Due within one year		173,917
Due after one year through five years		346,022
Due after five years through ten years		229,630
Due after ten years		395,588
Total before mortgage-backed securities		1,145,157
Total		2,142,472	2,425,477
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		1,702
Due after five years through ten years		64,115
Due after ten years		593,530
Total before mortgage-backed securities		659,347
Amortized Cost		659,347	675,674
Held-to-Maturity, Fair Value
Due within one year		0
Due after one year through five years		1,761
Due after five years through ten years		66,745
Due after ten years		609,989
Total before mortgage-backed securities		678,495
Total		678,495	$ 689,089
Mortgage-backed securities
Available-for-Sale, Amortized Cost
Mortgage-backed securities	[1]	996,135
Available-for-Sale, Fair Value
Mortgage-backed securities	[1]	997,315
Held-to-Maturity, Amortized Cost
Mortgage-backed securities	[1]	0
Held-to-Maturity, Fair Value
Mortgage-backed securities	[1]	$ 0

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