Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 2,830
Due from one year to five years	33,027
Due from five years to ten years	348,800
Due after ten years	731,279
Amortized cost, before securities without debt maturities	1,115,936
Amortized cost basis	2,465,029
Due in one year or less	0
Due from five years to ten years	0
Due from five years to ten years	0
Due after ten years	0
Amortized cost, before securities without debt maturities	0
Amortized cost basis	369,841	$ 606,679
Estimated Fair Value
Due in one year or less	2,830
Due from one year to five years	34,250
Due from five years to ten years	355,888
Due after ten years	739,242
Available for sale securities, debt maturities, before securities without single maturities	1,132,210
Estimated Fair Value	2,497,537	2,080,294
Due in one year or less	0
Due from one year to five years	0
Due from five years to ten years	0
Due after ten years	0
Held to maturity securities, before securities without single maturities	0
Debt Securities, Held-to-maturity	383,705
Residential mortgage-backed securities
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	177,183
Amortized cost basis	177,183
Held to maturity securities, amortized cost without single maturity date	369,841
Amortized cost basis	369,841	450,545
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	177,312
Estimated Fair Value	177,312
Held to maturity securities, without single maturities	383,705
Debt Securities, Held-to-maturity	383,705	$ 454,212
Collateralized mortgage obligations
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	682,307
Amortized cost basis	682,307
Held to maturity securities, amortized cost without single maturity date	0
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	693,718
Estimated Fair Value	693,718
Held to maturity securities, without single maturities	0
Residential mortgage-backed securities
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	489,603
Amortized cost basis	489,603
Held to maturity securities, amortized cost without single maturity date	0
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	494,297
Estimated Fair Value	494,297
Held to maturity securities, without single maturities	$ 0