INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities

The following table summarizes the amortized cost and estimated fair values of AFS and HTM securities, as of the dates indicated: 

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2018
AFS Investments (carried at fair value):
Obligations of states and political subdivisions	$	4,779	$	56	$	(3	)	$	4,832
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises	512,595		386		(17,713		)	495,268
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises	305,690		47		(12,383		)	293,354
Subordinated corporate bonds	5,485		82		(21		)	5,546
Total AFS investments	$	828,549	$	571	$	(30,120	)	$	799,000
HTM Investments (carried at amortized cost):
Obligations of states and political subdivisions	$	93,062	$	133	$	(1,594	)	$	91,601
Total HTM investments	$	93,062	$	133	$	(1,594	)	$	91,601
December 31, 2017
AFS Investments (carried at fair value):
Obligations of states and political subdivisions	$	7,232	$	103	$	—		$	7,335
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises	510,176		597		(7,471		)	503,302
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises	279,575		14		(6,790		)	272,799
Subordinated corporate bonds	5,484		173		—			5,657
Equity investments(1)	554		252		—			806
Total AFS investments	$	803,021	$	1,139	$	(14,261	)	$	789,899
HTM Investments (carried at amortized cost):
Obligations of states and political subdivisions	$	94,073	$	1,077	$	(237	)	$	94,913
Total HTM investments	$	94,073	$	1,077	$	(237	)	$	94,913

(1) As of December 31, 2017, equity investments were classified as AFS investments. Effective January 1, 2018, these investments were reclassified to other investments on the consolidated statements of condition as they are no longer eligible to be classified as AFS upon adoption of ASU 2016-01. Refer to Note 2 for further details.

The following table summarizes the cost and estimated fair values of the Company's investment in equity securities, FHLBB stock and FRBB stock as presented within other investments on the consolidated statements of condition, as of the dates indicated: 

	Cost		Unrealized Gains		Unrealized Losses		Fair Value
June 30, 2018
Equity securities - bank stock (carried at fair value)(1)	$	544	$	228	$	—	$	772
FHLBB (carried at cost)	20,196		—		—		20,196
FRB (carried at cost)	5,374		—		—		5,374
Total other investments	$	26,114	$	228	$	—	$	26,342
December 31, 2017
FHLBB (carried at cost)	$	18,296	$	—	$	—	$	18,296
FRB (carried at cost)	5,374		—		—		5,374
Total other investments	$	23,670	$	—	$	—	$	23,670

(1) Effective January 1, 2018, these investments were reclassified to other investments on the consolidated statements of condition as they are no longer eligible for AFS classification upon adoption of ASU 2016-01. Refer to Note 2 for further details.

Unrealized Gross Losses and Estimated Fair Values of Investment Securities by Length of Time that Individual Securities in Each Category in Continuous Loss Position

The following table presents the estimated fair values and gross unrealized losses on AFS and HTM investments that were in a continuous loss position at June 30, 2018 and December 31, 2017, by length of time that an individual security in each category has been in a continuous loss position:  

	Less Than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
June 30, 2018
AFS Investments:
Obligations of states and political subdivisions	$	1,517	$	(3	)	$	—	$	—		$	1,517	$	(3	)
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises	240,208		(6,256		)	240,607		(11,457		)	480,815		(17,713		)
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises	128,698		(2,837		)	149,438		(9,546		)	278,136		(12,383		)
Subordinated corporate bonds	964		(21		)	—		—			964		(21		)
Total AFS investments	$	371,387	$	(9,117	)	$	390,045	$	(21,003	)	$	761,432	$	(30,120	)
HTM Investments:
Obligations of states and political subdivisions	$	63,572	$	(1,119	)	$	10,229	$	(475	)	$	73,801	$	(1,594	)
Total HTM investments	$	63,572	$	(1,119	)	$	10,229	$	(475	)	$	73,801	$	(1,594	)
December 31, 2017
AFS Investments:
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises	$	221,466	$	(2,393	)	$	233,971	$	(5,078	)	$	455,437	$	(7,471	)
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises	102,612		(696		)	164,389		(6,094		)	267,001		(6,790		)
Total AFS investments	$	324,078	$	(3,089	)	$	398,360	$	(11,172	)	$	722,438	$	(14,261	)
HTM Investments:
Obligations of states and political subdivisions	$	9,317	$	(57	)	$	9,436	$	(180	)	$	18,753	$	(237	)
Total HTM investments	$	9,317	$	(57	)	$	9,436	$	(180	)	$	18,753	$	(237	)

Schedule of Sale of AFS Investments

The following table details the Company's sales of AFS investments for the period indicated below:

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2018		2017		2018		2017
Proceeds from sales of investments	$	9,898	$	—	$	9,898	$	—
Gross realized gains	31		—		31		—

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

The amortized cost and estimated fair values of the Company's AFS and HTM investments by contractual maturity at June 30, 2018, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. 

	Amortized Cost		Fair Value
AFS Investments
Due in one year or less	$	10,124	$	10,080
Due after one year through five years	116,798		113,751
Due after five years through ten years	195,301		187,899
Due after ten years	506,326		487,270
	$	828,549	$	799,000
HTM Investments
Due in one year or less	$	2,575	$	2,583
Due after one year through five years	3,598		3,626
Due after five years through ten years	17,022		16,924
Due after ten years	69,867		68,468
	$	93,062	$	91,601