Investment Securities (Tables)

12 Months Ended

Dec. 31, 2015

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:

	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
Corporate debt securities		—		—		—			—
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
	December 31, 2014
	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	$	71,144		4,001		(25	)	$	75,120
Obligations of states and political subdivisions		3,130		45		—			3,175
Corporate debt securities		1,891		17		—			1,908
Marketable equity securities		3,000		2		—			3,002
Total securities available for sale	$	79,165	$	4,065	$	(25	)	$	83,205
Securities Held to Maturity
Obligations of U.S. government corporations and agencies	$	660,836		13,055		(677	)	$	673,214
Obligations of states and political subdivisions		15,590		130		(155	)		15,565
Total securities held to maturity	$	676,426	$	13,185	$	(832	)	$	688,779

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	$	8,870	$	9,112	$	1,147	$	1,158
Due after five years through ten years		24,150		25,204		830		870
Due after ten years		369,720		370,569		724,553		730,181
Totals	$	402,740	$	404,885	$	726,530	$	732,209

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
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
	(in thousands)
December 31, 2015
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	)
	Less than 12 months					12 months or more					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
	(in thousands)
December 31, 2014
Securities Available for Sale:
Obligations of U.S. government corporations and agencies	$	6,774	$	(25	)		—		—		$	6,774	$	(25	)
Obligations of states and political subdivisions		—		—			—		—			—		—
Marketable equity securities		—		—			—		—			—		—
Total securities available-for-sale	$	6,774	$	(25	)		—		—		$	6,774	$	(25	)
Securities Held to Maturity:
Obligations of U.S. government corporations and agencies	$	335	$	(1	)	$	56,288	$	(676	)	$	56,623	$	(677	)
Obligations of states and political subdivisions		1,600		(26	)		1,858		(129	)		3,458		(155	)
Total securities held-to-maturity	$	1,935	$	(27	)	$	58,146	$	(805	)	$	60,081	$	(832	)