Investment Securities (Tables)

12 Months Ended

Dec. 31, 2016

Amortized Cost and Estimated Fair Values of Investments in Debt and Equity Securities

The amortized cost and estimated fair values of investments in debt and equity securities are summarized in the following tables:


	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Securities Available for Sale
Obligations of U.S. government corporations and agencies	$	434,357	$	1,949	$	(6,628	)	$	429,678
Obligations of states and political subdivisions		121,746		267		(4,396	)		117,617
Marketable equity securities		3,000		—		(62	)		2,938

Total securities available for sale	$	559,103	$	2,216	$	(11,086	)	$	550,233

Securities Held to Maturity
Obligations of U.S. government corporations and agencies	$	587,982	$	5,001	$	(4,199	)	$	588,784
Obligations of states and political subdivisions		14,554		56		(191	)		14,419

Total securities held to maturity	$	602,536	$	5,057	$	(4,390	)	$	603,203


	December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Securities Available for Sale
Obligations of U.S. government corporations and agencies	$	312,917	$	2,761	$	(1,996	)	$	313,682
Obligations of states and political subdivisions		86,823		1,428		(33	)		88,218
Marketable equity securities		3,000		—		(15	)		2,985

Total securities available for sale	$	402,740	$	4,189	$	(2,044	)	$	404,885

Securities Held to Maturity
Obligations of U.S. government corporations and agencies	$	711,994	$	8,394	$	(2,882	)	$	717,506
Obligations of states and political subdivisions		14,536		277		(110	)		14,703

Total securities held to maturity	$	726,530	$	8,671	$	(2,992	)	$	732,209

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

For purposes of the following table, the entire outstanding balance of these mortgage-backed securities issued by U.S. government corporations and agencies is categorized based on final maturity date.


Investment Securities (In thousands)	Available for Sale				Held to Maturity
Investment Securities (In thousands)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year	$	1	$	1		—		—
Due after one year through five years		9,392		9,650	$	1,177	$	1,185
Due after five years through ten years		14,548		15,132		4,776		4,762
Due after ten years		535,162		525,450		596,583		597,256

Totals	$	559,103	$	550,233	$	602,536	$	603,203

Gross Unrealized Losses on Investment

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, were as follows:


	Less than 12 months					12 months or more					Total
December 31, 2016	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
	(in thousands)
Securities Available for Sale:
Obligations of U.S. government corporations and agencies	$	370,389	$	(6,628	)		—		—		$	370,389	$	(6,628	)
Obligations of states and political subdivisions		90,825		(4,396	)		—		—			90,825		(4,396	)
Marketable equity securities		2,938		(62	)		—		—			2,938		(62	)

Total securities available-for-sale	$	464,152	$	(11,086	)		—		—		$	464,152	$	(11,086	)

Securities Held to Maturity:
Obligations of U.S. government corporations and agencies	$	280,497	$	(4,199	)		—		—		$	280,497	$	(4,199	)
Obligations of states and political subdivisions		9,984		(191	)		—		—			9,984		(191	)

Total securities held-to-maturity	$	290,481	$	(4,390	)		—		—		$	290,481	$	(4,390	)


	Less than 12 months					12 months or more					Total
December 31, 2015	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
	(in thousands)
Securities Available for Sale:
Obligations of U.S. government corporations and agencies	$	193,306	$	(1,996	)		—		—		$	193,306	$	(1,996	)
Obligations of states and political subdivisions		6,469		(33	)		—		—			6,469		(33	)
Marketable equity securities		2,985		(15	)		—		—			2,985		(15	)

Total securities available-for-sale	$	202,760	$	(2,044	)		—		—		$	202,760	$	(2,044	)

Securities Held to Maturity:
Obligations of U.S. government corporations and agencies	$	198,481	$	(2,882	)		—		—		$	198,481	$	(2,882	)
Obligations of states and political subdivisions		497		(11	)	$	1,121	$	(99	)		1,618		(110	)

Total securities held-to-maturity	$	198,978	$	(2,893	)	$	1,121	$	(99	)	$	200,099	$	(2,992	)