Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Available for Sale
Due in one year or less	$ 11,250
Due from one year to five years	39,069
Due from five years to ten years	327,456
Due after ten years	963,453
Amortized cost, before securities without debt maturities	1,341,228
Amortized Cost	2,947,500
Estimated Fair Value
Due in one year or less	11,350
Due from one year to five years	40,717
Due from five years to ten years	345,612
Due after ten years	1,020,285
Available for sale securities, debt maturities, before securities without single maturities	1,417,964
Estimated Fair Value	3,062,143	$ 2,497,537
Amortized Cost
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
Debt securities, held-to-maturity, maturity, allocated and single maturity date, amortized cost, total	0
Amortized Cost, Held to Maturity	278,281	369,841
Estimated Fair Value
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
Debt securities, held-to-maturity, maturity, Allocated and single maturity date, fair value	0
Estimated Fair Value, Held to Maturity	296,857
Collateralized mortgage obligations
Available for Sale
Available-for-sale securities, amortized cost without single maturity date	491,321
Amortized Cost	491,321
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	503,766
Estimated Fair Value	503,766
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	0
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	0
Commercial mortgage-backed securities
Available for Sale
Available-for-sale securities, amortized cost without single maturity date	741,172
Amortized Cost	741,172
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	762,415
Estimated Fair Value	762,415
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	0
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	0
Residential mortgage-backed securities
Available for Sale
Available-for-sale securities, amortized cost without single maturity date	373,779
Amortized Cost	373,779
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	377,998
Estimated Fair Value	377,998
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	278,281
Amortized Cost, Held to Maturity	278,281	369,841
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	296,857
Estimated Fair Value, Held to Maturity	$ 296,857	$ 383,705