Debt Securities Maturity Schedule (Details) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019
Available-for-Sale, Amortized Cost
Due within one year		$ 144,070
Due after one year through five years		269,452
Due after five years through ten years		261,463
Due after ten years		950,305
Total before mortgage-backed securities		1,625,290
Total		3,359,493	$ 2,521,374
Available-for-Sale, Fair Value
Due within one year		145,977
Due after one year through five years		281,526
Due after five years through ten years		275,179
Due after ten years		1,016,343
Total before mortgage-backed securities		1,719,025
Debt securities, available-for-sale		3,533,950	2,575,252
Held-to-Maturity, Amortized Cost
Due within one year		0
Due after one year through five years		17,132
Due after five years through ten years		71,471
Due after ten years		114,672
Total before mortgage-backed securities		203,275
Amortized Cost		203,275	224,611
Held-to-Maturity, Fair Value
Due within one year		0
Due after one year through five years		18,339
Due after five years through ten years		76,970
Due after ten years		120,574
Total before mortgage-backed securities		215,883
Total		215,883	$ 234,396
Mortgage-backed securities
Available-for-Sale, Amortized Cost
Mortgage-backed securities	[1]	1,734,203
Available-for-Sale, Fair Value
Mortgage-backed securities	[1]	1,814,925
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.