Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized cost within one year	$ 49,129	$ 37,386
Amortized cost one to five years	49,766	41,230
Amortized cost for five to ten years	112,483	117,004
Amortized cost for after ten years	457,005	213,574
Available for sale	668,383	409,194
Amortized Cost	976,813	822,089
Within one year, amortized cost	8,205	7,811
One to five years, amortized cost	46,090	56,037
Five to ten years, amortized cost	85,339	94,756
After ten years, amortized cost	26,224	32,163
Total amortized cost	165,858	190,767
Investment securities, held to maturity	180,270	207,899
Fair value within one year	49,088	37,321
Fair value for one to five years	51,201	41,293
Fair value for five to ten years	121,648	122,145
Fair value for after ten years	475,085	218,193
Total fair value	697,022	418,952
Within one year, fair value	8,245	7,874
One to five years, fair value	47,750	57,048
five to ten years, fair value	91,579	98,480
After ten years, fair value	29,203	34,440
Total fair value	176,777	197,842
Fair Value	191,612	215,147
Fair Value	1,015,343	834,776
Federal agency collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available for sale	180,628	267,272
Amortized Cost	180,628	267,272
Investment securities, held to maturity	2,839	4,560
Fair Value	2,906	4,568
Fair Value	185,849	269,252
Federal agency mortgage-backed pools
Schedule of Available-for-sale Securities [Line Items]
Available for sale	127,802	145,623
Amortized Cost	127,802	145,623
Investment securities, held to maturity	11,573	12,572
Fair Value	11,929	12,737
Fair Value	$ 132,472	$ 146,572

Available for sale securities debt maturities rolling fair value.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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