Investment Securities (Tables)

6 Months Ended

Jun. 30, 2016

Investments, Debt and Equity Securities [Abstract]

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:

	June 30, 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	$	398,811	$	10,175		—		$	408,986
Obligations of states and political subdivisions		111,763		5,221		—			116,984
Marketable equity securities		3,000		47		—			3,047
Total securities available for sale	$	513,574	$	15,443		—		$	529,017
Securities Held to Maturity
Obligations of U.S. government corporations and agencies	$	659,867	$	24,532		—		$	684,399
Obligations of states and political subdivisions		14,545		655		—			15,200
Total securities held to maturity	$	674,412	$	25,187		—		$	699,599
	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	Available for Sale				Held to Maturity
(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		12,246		12,748	$	1,161	$	1,201
Due after five years through ten years		16,676		17,557		845		936
Due after ten years		484,651		498,711		672,406		697,462
Totals	$	513,574	$	529,017	$	674,412	$	699,599

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
June 30, 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		—		—			—		—			—		—
Obligations of states and political subdivisions		—		—			—		—			—		—
Marketable equity securities		—		—			—		—			—		—
Total securities available-for-sale		—		—			—		—			—		—
Securities Held to Maturity:
Obligations of U.S. government corporations and agencies		—		—			—		—			—		—
Obligations of states and political subdivisions		—		—			—		—			—		—
Total securities held-to-maturity		—		—			—		—			—		—
	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	)