Investment Securities Available-for-Sale (Tables)

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of amortized cost and estimated fair value of securities available-for-sale

Amortized cost and estimated fair value of securities available-for-sale are summarized as follows:

December 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for		Estimated Fair Value
(dollars in thousands)							Credit Losses
U. S. agency securities	$	181,087	$	1,461	$	(627)	$	—	$	181,921
Residential mortgage backed securities	811,328		14,506		(833)		—		825,001
Municipal bonds	102,259		5,872		—		(18)		108,113
Corporate bonds	34,383		1,624		(8)		(149)		35,850
	$	1,129,057	$	23,463	$	(1,468)	$	(167)	$	1,150,885

December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
(dollars in thousands)
U. S. agency securities	$	180,228	$	621	$	(1,055)	$	179,794
Residential mortgage backed securities	541,490		4,337		(1,975)		543,852
Municipal bonds	71,902		2,034		(5)		73,931
Corporate bonds	10,530		203		—		10,733
U.S. Treasury	34,844		11		—		34,855
	$	838,994	$	7,206	$	(3,035)	$	843,165

Schedule of gross unrealized losses and fair value by length of time that the individual available-for-sale securities have been in a continuous unrealized loss

Gross unrealized losses and fair value by length of time that the individual available-for-sale securities have been in a continuous unrealized loss position as of December 31, 2020 and 2019 are as follows:

		Less than 12 Months				12 Months or Greater				Total
December 31, 2020	Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
(dollars in thousands)
U. S. agency securities	28	$	46,412	$	67	$	41,320	$	560	$	87,732	$	627
Residential mortgage backed securities	35	170,178		782		6,419		51		176,597		833
Corporate bonds	3	5,764		8		—		—		5,764		8
	66	$	222,354	$	857	$	47,739	$	611	$	270,093	$	1,468

		Less than 12 Months				12 Months or Greater				Total
December 31, 2019	Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
(dollars in thousands)
U. S. agency securities	36	$	75,159	$	439	$	51,481	$	616	$	126,640	$	1,055
Residential mortgage backed securities	111	197,794		1,148		90,742		827		288,536		1,975
Municipal bonds	1	1,994		5		—		—		1,994		5
	148	$	274,947	$	1,592	$	142,223	$	1,443	$	417,170	$	3,035

Schedule of amortized cost and estimated fair value of investments available-for-sale by contractual maturity

The amortized cost and estimated fair value of investments available-for-sale at December 31, 2020 and 2019 by contractual maturity are shown in the table below. Expected maturities for residential mortgage backed securities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	December 31, 2020				December 31, 2019
(dollars in thousands)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
U. S. agency securities maturing:
One year or less	$	53,916	$	53,906	$	96,332	$	96,226
After one year through five years	110,083		110,777		76,121		75,821
Five years through ten years	17,087		17,240		7,775		7,747
Residential mortgage backed securities	811,328		825,001		541,490		543,852
Municipal bonds maturing:
One year or less	4,329		4,348		5,897		5,969
After one year through five years	26,622		28,272		21,416		21,953
Five years through ten years	69,309		73,389		42,589		44,015
After ten years	2,000		2,121		2,000		1,994
Corporate bonds maturing:
One year or less	5,218		5,220		502		508
After one year through five years	22,189		23,267		8,528		8,725
Five years through ten years	6,976		7,511		—		—
After ten years	—		—		1,500		1,500
U.S. treasury	—		—		34,844		34,855
Allowance for credit losses	—		(167)		—		—
	$	1,129,057	$	1,150,885	$	838,994	$	843,165