Investment Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of investment securities available-for-sale

The following table shows investment securities available-for-sale.



(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
March 31, 2018
U.S. Treasury and Federal agencies securities	$	510,739	$	7	$	(7,749	)	$	502,997
U.S. States and political subdivisions securities	98,740		321		(1,076		)	97,985
Mortgage-backed securities — Federal agencies	301,717		997		(6,384		)	296,330
Corporate debt securities	44,584		—		(528		)	44,056
Foreign government and other securities	700		8		—			708
Total debt securities available-for-sale	$	956,480	$	1,333	$	(15,737	)	$	942,076

December 31, 2017
U.S. Treasury and Federal agencies securities	$	471,508	$	57	$	(3,446	)	$	468,119
U.S. States and political subdivisions securities	116,260		648		(908		)	116,000
Mortgage-backed securities — Federal agencies	289,327		1,456		(2,873		)	287,910
Corporate debt securities	31,573		5		(284		)	31,294
Foreign government and other securities	700		10		—			710
Total debt securities available-for-sale	$	909,368	$	2,176	$	(7,511	)	$	904,033

Schedule of contractual maturities of investments in debt securities available-for-sale

The following table shows the contractual maturities of investments in debt securities available-for-sale at March 31, 2018. Expected maturities will differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.



(Dollars in thousands)	Amortized Cost		Fair Value
Due in one year or less	$	73,984	$	73,935
Due after one year through five years	560,259		551,743
Due after five years through ten years	20,520		20,068
Due after ten years	—		—
Mortgage-backed securities	301,717		296,330
Total debt securities available-for-sale	$	956,480	$	942,076

Schedule of gross unrealized losses and fair value by investment category and age

The following table summarizes gross unrealized losses and fair value by investment category and age.



	Less than 12 Months					12 months or Longer					Total
(Dollars in thousands)	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
March 31, 2018
U.S. Treasury and Federal agencies securities	$	399,359	$	(4,388	)	$	88,465	$	(3,361	)	$	487,824	$	(7,749	)
U.S. States and political subdivisions securities	46,927		(484		)	18,067		(592		)	64,994		(1,076		)
Mortgage-backed securities - Federal agencies	175,903		(3,672		)	67,169		(2,712		)	243,072		(6,384		)
Corporate debt securities	34,146		(184		)	9,910		(344		)	44,056		(528		)
Foreign government and other securities	—		—			—		—			—		—
Total debt securities available-for-sale	$	656,335	$	(8,728	)	$	183,611	$	(7,009	)	$	839,946	$	(15,737	)

December 31, 2017
U.S. Treasury and Federal agencies securities	$	311,865	$	(1,161	)	$	89,617	$	(2,285	)	$	401,482	$	(3,446	)
U.S. States and political subdivisions securities	34,971		(287		)	24,909		(621		)	59,880		(908		)
Mortgage-backed securities - Federal agencies	137,169		(1,336		)	60,162		(1,537		)	197,331		(2,873		)
Corporate debt securities	13,747		(57		)	10,048		(227		)	23,795		(284		)
Foreign government and other securities	—		—			—		—			—		—
Total debt securities available-for-sale	$	497,752	$	(2,841	)	$	184,736	$	(4,670	)	$	682,488	$	(7,511	)

Schedule of gross realized gains and losses from securities available-for-sale portfolio

The following table shows the gross realized gains and losses from the securities available-for-sale portfolio, including marketable equity securities. Realized gains and losses of all securities are computed using the specific identification cost basis.



	Three Months Ended March 31,
(Dollars in thousands)	2018			2017
Gross realized gains	$	2		$	1,285
Gross realized losses	(347		)	—
OTTI losses	—			—
Net realized gains (losses)	$	(345	)	$	1,285