Investment in Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Investment Securities

The amortized cost, gross unrealized gains, gross unrealized losses and fair value of investment securities are summarized as follows:

	March 31, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized
(In thousands)	Cost		Gains		Losses		Fair Value
State and political subdivisions	$	395,439	$	3,582	$	3,681	$	395,340
U.S. government agencies		53,943		—		1,543		52,400
Certificates of deposit		7,241		—		—		7,241
Total	$	456,623	$	3,582	$	5,224	$	454,981

	December 31, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized
(In thousands)	Cost		Gains		Losses		Fair Value
State and political subdivisions	$	408,165	$	9,528	$	661	$	417,032
U.S. government agencies		46,222		—		722		45,500
Certificates of deposit		7,991		—		—		7,991
Total	$	462,378	$	9,528	$	1,383	$	470,523

Schedule of the Fair Value of Securities with Unrealized Losses

The fair values of securities with unrealized losses are as follows:

	March 31, 2018
	Less than 12 months				12 months or more				Total
	Estimated		Unrealized		Estimated		Unrealized		Estimated		Unrealized
(In thousands)	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
State and political subdivisions	$	171,575	$	2,364	$	30,324	$	1,317	$	201,900	$	3,681
U.S. government agencies		41,626		992		10,775		551		52,400		1,543
Certificates of deposit		—		—		—		—		—		—
Total	$	213,201	$	3,356	$	41,099	$	1,868	$	254,300	$	5,224

	December 31, 2017
	Less than 12 months				12 months or more				Total
	Estimated		Unrealized		Estimated		Unrealized		Estimated		Unrealized
(In thousands)	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
State and political subdivisions	$	34,755	$	123	$	31,251	$	538	$	66,006	$	661
U.S. government agencies		34,183		376		11,317		346		45,500		722
Certificates of deposit		—		—		—		—		—		—
Total	$	68,938	$	499	$	42,568	$	884	$	111,506	$	1,383

Schedule of Amortized Cost and Fair Value of Investment

The amortized cost and fair value of investment securities by contractual maturity are shown in the following table. Expected maturities may differ from contractual maturities because borrowers have the right to prepay obligations with or without prepayment penalties.

	March 31, 2018
(In thousands)	Amortized Cost		Fair Value
Due in 1 year or less	$	16,224	$	16,320
Due after 1 year through 5 years		64,485		64,887
Due after 5 years through 10 years		253,486		254,514
Due after 10 years		122,428		119,260
Total	$	456,623	$	454,981