Debt Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Available-for-Sale, Amortized Cost
Due within one year		$ 62,317
Due after one year through five years		170,631
Due after five years through ten years		206,056
Due after ten years		459,230
Total before mortgage-backed securities		898,234
Amortized Cost		2,521,374	$ 2,580,520
Available-for-Sale, Fair Value
Due with one year		62,555
Due after one year through five years		174,195
Due after five years through ten years		214,517
Due after ten years		472,454
Total before mortgage-backed securities		923,721
Total		2,575,252	2,571,663
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		12,841
Due after five years through ten years		71,708
Due after ten years		140,062
Total before mortgage-backed securities		224,611
Amortized Cost		224,611	297,915
Held-to-Maturity, Fair Value
Due within one year		0
Due after one year through five years		13,383
Due after five years through ten years		75,771
Due after ten years		145,242
Total before mortgage-backed securities		234,396
Total		234,396	$ 288,256
Mortgage-backed securities
Available-for-Sale, Amortized Cost
Mortgage-backed securities	[1]	1,623,140
Available-for-Sale, Fair Value
Mortgage-backed securities	[1]	1,651,531
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.