Debt Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Available-for-Sale, Amortized Cost
Due within one year		$ 50,668
Due after one year through five years		241,525
Due after five years through ten years		285,233
Due after ten years		409,614
Total before mortgage-backed securities		987,040
Total		2,403,517	$ 2,580,520
Available-for-Sale, Fair Value
Due within one year		50,748
Due after one year through five years		245,014
Due after five years through ten years		298,290
Due after ten years		425,262
Total before mortgage-backed securities		1,019,314
Debt securities, available-for-sale		2,470,634	2,571,663
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		8,391
Due after five years through ten years		78,886
Due after ten years		164,820
Total before mortgage-backed securities		252,097
Amortized Cost		252,097	297,915
Held-to-Maturity, Fair Value
Due within one year		0
Due after one year through five years		8,678
Due after five years through ten years		82,526
Due after ten years		169,490
Total before mortgage-backed securities		260,694
Total		260,694	$ 288,256
Mortgage-backed securities
Available-for-Sale, Amortized Cost
Mortgage-backed securities	[1]	1,416,477
Available-for-Sale, Fair Value
Mortgage-backed securities	[1]	1,451,320
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.