Investment Securities (Tables)

9 Months Ended

Sep. 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:

	September 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	$	377,072	$	9,800		—		$	386,872
Obligations of states and political subdivisions		116,752		3,634	$	(82	)		120,304
Marketable equity securities		3,000		33		—			3,033
Total securities available for sale	$	496,824	$	13,467	$	(82	)	$	510,209
Securities Held to Maturity
Obligations of U.S. government corporations and agencies	$	626,599	$	22,145		—		$	648,744
Obligations of states and political subdivisions		14,550		487		—			15,037
Total securities held to maturity	$	641,149	$	22,632		—		$	663,781

	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		—		—		—		—
Due after one year through five years	$	10,578	$	10,969	$	1,169	$	1,203
Due after five years through ten years		15,637		16,397		853		943
Due after ten years		470,609		482,843		639,127		661,635
Totals	$	496,824	$	510,209	$	641,149	$	663,781

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
September 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	$	9,521	$	(82	)		—		—		$	9,521	$	(82	)
Marketable equity securities		—		—			—		—			—		—
Total securities available-for-sale	$	9,521	$	(82	)		—		—		$	9,521	$	(82	)
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	)