Investment securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost of Securities and Fair Values

The amortized cost of securities and their fair values at March 31, 2018 and December 31, 2017 are shown below:

	March 31, 2018
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Investment Securities
Available-for-sale debt securities
U.S. government agency securities	$	999	$	—	$	(17	)	$	982
Mortgage-backed securities - residential		486,907		237		(14,214	)		472,930
Municipals, tax exempt		113,492		1,582		(1,916	)		113,158
Treasury securities		7,356		—		(178	)		7,178
Total	$	608,754	$	1,819	$	(16,325	)	$	594,248

	December 31, 2017
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair Value
Investment Securities
Available-for-sale debt securities
U.S. government agency securities	$	999	$	—	$	(13	)	$	986
Mortgage-backed securities - residential		425,557		374		(7,150	)		418,781
Municipals, tax exempt		107,127		2,692		(568	)		109,251
Treasury securities		7,345		—		(93	)		7,252
Total debt securities		541,028		3,066		(7,824	)		536,270
Equity and other securities		7,870		1		(149	)		7,722
Total investment securities	$	548,898	$	3,067	$	(7,973	)	$	543,992

Schedule of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

Therefore, mortgage-backed securities are not included in the maturity categories in the following maturity summary.

	March 31, 2018				December 31, 2017
	Available-for-sale				Available-for-sale
	Amortized cost		Fair value		Amortized cost		Fair value
Due in one year or less	$	5,715	$	5,841	$	905	$	925
Due in one to five years		24,165		24,396		28,332		28,878
Due in five to ten years		19,817		19,960		19,218		19,588
Due in over ten years		72,150		71,121		67,016		68,098
		121,847		121,318		115,471		117,489
Mortgage-backed securities - residential		486,907		472,930		425,557		418,781
Total debt securities	$	608,754	$	594,248	$	541,028	$	536,270

Summary of Sales and Impairment of Available-for-Sale Securities

Sales and impairment of available-for-sale securities were as follows:

	Three Months Ended March 31,
	2018		2017
Proceeds from sales	$	221	$	—
Gross realized gains		—		—
Gross realized losses		9		—

Schedule of Gross Unrealized Losses

The following tables show gross unrealized losses at March 31, 2018 and December 31, 2017, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position:

	March 31, 2018
	Less than 12 months				12 months or more				Total
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized loss
U.S. government agency securities	$	—	$	—	$	982	$	17	$	982	$	17
Mortgage-backed securities - residential		163,771		3,236		274,285		10,978		438,056		14,214
Municipals, tax exempt		30,104		762		19,186		1,154		49,290		1,916
Treasury securities		7,177		178		—		—		7,177	$	178
Total debt securities	$	201,052	$	4,176	$	294,453	$	12,149	$	495,505	$	16,325

	December 31, 2017
	Less than 12 months				12 months or more				Total
	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized loss
U.S. government agency securities	$	—	$	—	$	986	$	13	$	986	$	13
Mortgage-backed securities - residential		107,611		980		290,258		6,170		397,869		7,150
Municipals, tax exempt		7,354		101		20,112		467		27,466		568
Treasury securities		7,252		93		—		—		7,252		93
Total debt securities		122,217		1,174		311,356		6,650		433,573		7,824
Equity securities		—		—		3,050		149		3,050		149
	$	122,217	$	1,174	$	314,406	$	6,799	$	436,623	$	7,973