Investment Securities Available-for-Sale (Tables)

9 Months Ended

Sep. 30, 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:

​	​		Gross		Gross		Allowance		Estimated
September 30, 2020	Amortized		Unrealized		Unrealized		for Credit		Fair
(dollars in thousands)	Cost		Gains		Losses		Losses		Value
U.S. agency securities	$	130,313	$	1,638	$	(665)	$	—	$	131,286
Residential mortgage backed securities	702,655		14,578		(590)		—		716,643
Municipal bonds	90,292		4,551		(114)		(16)		94,713
Corporate bonds	33,345		1,596		(71)		(140)		34,730
Other equity investments	198		—		—		—		198
​	$	956,803	$	22,363	$	(1,440)	$	(156)	$	977,570

​	​		Gross		Gross		Estimated
December 31, 2019	Amortized		Unrealized		Unrealized		Fair
(dollars in thousands)	Cost		Gains		Losses		Value
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
Other equity investments	198		—		—		198
​	$	839,192	$	7,206	$	(3,035)	$	843,363

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 of available-for-sale securities for which an allowance for credit losses has not been recorded, by length of time that individual securities have been in a continuous unrealized loss position are as follows:

​	​	Less than				12 Months				​		​
​	​	12 Months				or Greater				Total
​	​	Estimated		​		Estimated		​		Estimated		​
September 30, 2020	Number of	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(dollars in thousands)	Securities	Value		Losses		Value		Losses		Value		Losses
U. S. agency securities	25	$	20,762	$	32	$	43,607	$	633	$	64,369	$	665
Residential mortgage backed securities	33	139,848		549		7,334		41		147,182		590
Municipal bonds	4	14,086		114		—		—		14,086		114
Corporate bonds	1	2,954		71		—		—		2,954		71
​	63	$	177,650	$	766	$	50,941	$	674	$	228,591	$	1,440

​	​	Less than				12 Months				​		​
​	​	12 Months				or Greater				Total
​	​	Estimated		​		Estimated		​		Estimated		​
December 31, 2019	Number of	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(dollars in thousands)	Securities	Value		Losses		Value		Losses		Value		Losses
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

​	September 30, 2020				December 31, 2019
​	Amortized		Estimated		Amortized		Estimated
(dollars in thousands)	Cost		Fair Value		Cost		Fair Value
U. S. agency securities maturing:	​		​		​		​
One year or less	$	38,000	$	38,111	$	96,332	$	96,226
After one year through five years	81,181		82,057		76,121		75,821
Five years through ten years	11,132		11,224		7,775		7,747
Residential mortgage backed securities	702,655		716,643		541,490		543,852
Municipal bonds maturing:
One year or less	4,834		4,868		5,897		5,969
After one year through five years	26,677		27,912		21,416		21,953
Five years through ten years	56,781		59,771		42,589		44,015
After ten years	2,000		2,072		2,000		1,994
Corporate bonds maturing:
One year or less	5,214		5,257		502		508
After one year through five years	21,156		22,124		8,528		8,725
After ten years	6,975		7,489		1,500		1,500
U.S. treasury	—		—		34,844		34,855
Other equity investments	198		198		198		198
Allowance for Credit Losses	—		(156)		—		—
​	$	956,803	$	977,570	$	839,192	$	843,363