Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized cost within one year	$ 46,747	$ 44,206
Amortized cost one to five years	156,088	61,594
Amortized cost for five to ten years	362,439	136,857
Amortized cost for after ten years	802,546	589,200
Available for sale	1,367,820	831,857
Amortized Cost	1,662,254	1,090,363
Within one year, amortized cost	4,314	7,302
One to five years, amortized cost	43,418	42,742
Five to ten years, amortized cost	73,870	82,087
After ten years, amortized cost	22,828	25,290
Total amortized cost	144,430	157,421
Investment securities, held to maturity	153,284	168,676
Fair value within one year	46,784	44,192
Fair value for one to five years	157,620	63,006
Fair value for five to ten years	366,313	145,102
Fair value for after ten years	820,769	615,473
Total fair value	1,391,486	867,773
Investment securities, available for sale	1,691,186	1,134,025
Within one year, fair value	4,349	7,327
One to five years, fair value	44,942	44,358
Five to ten years, fair value	78,956	88,300
After ten years, fair value	25,359	28,471
Total fair value	153,606	168,456
Fair Value	162,651	179,990
Federal agency collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available for sale	96,344	144,022
Amortized Cost	96,344	144,022
Investment securities, held to maturity	1,007	2,661
Investment securities, available for sale	98,622	147,453
Fair Value	1,023	2,697
Federal agency mortgage-backed pools
Schedule of Available-for-sale Securities [Line Items]
Available for sale	165,016	114,484
Amortized Cost	165,016	114,484
Investment securities, held to maturity	3,733	8,594
Investment securities, available for sale	167,510	118,799
Fair Value	3,908	8,837
Private labeled mortgage-backed pools
Schedule of Available-for-sale Securities [Line Items]
Available for sale	33,074	0
Amortized Cost	33,074
Investment securities, held to maturity	4,114	0
Investment securities, available for sale	33,568	0
Fair Value	$ 4,114	$ 0

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