Investment Securities Available-for-Sale (Tables)

9 Months Ended

Sep. 30, 2018

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:

September 30, 2018 (dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
U. S. agency securities	$	236,853	$	—	$	6,528	$	230,325
Residential mortgage backed securities		448,335		140		12,126		436,349
Municipal bonds		48,203		391		858		47,736
Corporate bonds		8,004		61		19		8,046
Other equity investments		218		—		—		218
	$	741,613	$	592	$	19,531	$	722,674

December 31, 2017 (dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
U. S. agency securities	$	198,115	$	283	$	2,414	$	195,984
Residential mortgage backed securities		322,067		187		4,418		317,836
Municipal bonds		60,976		1,295		214		62,057
Corporate bonds		13,010		163		—		13,173
Other equity investments		218		—		—		218
	$	594,386	$	1,928	$	7,046	$	589,268

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 position

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 are as follows:

			Less than 12 Months				12 Months or Greater				Total
September 30, 2018 (dollars in thousands)	Number of Securities		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
U. S. agency securities		61	$	111,702	$	1,909	$	115,678	$	4,619	$	227,380	$	6,528
Residential mortgage backed securities		184		237,720		3,938		190,668		8,188		428,388		12,126
Municipal bonds		16		16,388		352		10,440		506		26,828		858
Corporate bonds		2		2,981		19		—		—		2,981		19
		263	$	368,791	$	6,218	$	316,786	$	13,313	$	685,577	$	19,531

			Less than 12 Months				12 Months or Greater				Total
December 31, 2017 (dollars in thousands)	Number of Securities		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
U. S. agency securities		38	$	102,264	$	1,073	$	55,093	$	1,341	$	157,357	$	2,414
Residential mortgage backed securities		137		152,350		1,306		147,953		3,112		300,303		4,418
Municipal bonds		8		17,446		214		—		—		17,446		214
		183	$	272,060	$	2,593	$	203,046	$	4,453	$	475,106	$	7,046

Schedule of available-for-sale securities by contractual maturity

The amortized cost and estimated fair value of investments available-for-sale at September 30, 2018 and December 31, 2017 by contractual maturity are shown in the table below.

	September 30, 2018				December 31, 2017
(dollars in thousands)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
U. S. agency securities maturing:
One year or less	$	119,017	$	114,692	$	109,893	$	108,198
After one year through five years		104,464		102,953		74,106		73,916
Five years through ten years		13,372		12,680		14,116		13,870
Residential mortgage backed securities		448,335		436,349		322,067		317,836
Municipal bonds maturing:
One year or less		9,882		9,969		5,068		5,171
After one year through five years		15,579		15,541		19,405		19,879
Five years through ten years		21,675		21,094		35,432		35,846
After ten years		1,067		1,132		1,071		1,161
Corporate bonds maturing:
After one year through five years		6,504		6,546		11,510		11,673
After ten years		1,500		1,500		1,500		1,500
Other equity investments		218		218		218		218
	$	741,613	$	722,674	$	594,386	$	589,268