Retirement Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Matching obligations, in connection with plans which are funded in cash and typically contributed to plans [Abstract]
Defined contribution plan, recognized	$ 8,267,000	$ 8,115,000	$ 8,100,000
Employer contributions during the period	500,000	400,000	500,000
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Provision for expense in connection with ESOP	1,800,000	4,400,000	3,900,000
Employee Stock Ownership Plan and Trust (ESOP) [Member]
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Additional shares contributed to ESOP (in shares)	58,570
Shares released from trust (in shares)	58,600
Total remaining balance of shares in the ESOP (in shares)	400
SERP Defined Benefit Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	5,661,000	4,725,000
Service cost	164,000	180,000	130,000
Interest cost	277,000	235,000	186,000
Actuarial loss	436,000	521,000
Benefit obligation at end of year	6,538,000	5,661,000	4,725,000
Unfunded status of the plan	(6,538,000)	(5,661,000)
Amounts recognized in the balance sheet [Abstract]
Accrued postretirement benefit liabilities	6,538,000	5,661,000
Accumulated other comprehensive loss (pre-tax) related to [Abstract]
Unrecognized net actuarial losses	1,389,000	1,342,000
Unrecognized prior service cost	0	0
Summary of defined benefit plan amounts were included in other comprehensive income [Abstract]
Actuarial gains (losses) ,Incurred but Not Recognized	261,000
Prior service (cost) credit, ,Incurred but Not Recognized	0
Benefit plans, before reclassification adjustments, Incurred but Not Recognized	261,000
Actuarial gains (losses), Reclassification Adjustment for Prior Period Amounts Recognized	233,000
Prior service (cost) credit, Reclassification Adjustment for Prior Period Amounts Recognized	0
Benefit plans, after reclassification adjustments, Reclassification Adjustment for Prior Period Amounts Recognized	233,000
Prior service cost (credit) included in accumulated other comprehensive income expected to be recognized in net periodic benefit cost during 2015	700,000
Prior service cost (credit) expected to be amortized from accumulated other comprehensive income	400,000
Defined benefit retirement plan [Abstract]
Service cost	164,000	180,000	130,000
Interest cost	277,000	235,000	186,000
Amortization of prior service cost	0	28,000	110,000
Amortization of unrecognized loss	388,000	690,000	261,000
Net periodic benefit cost	829,000	1,133,000	687,000
Actuarial assumptions used to determine costs and benefit obligations [Abstract]
Discount rates (in hundredths)	4.00%	4.90%	4.00%
Salary increase (in hundredths)		4.00%	4.00%
Summary of defined benefit pension plan, the projected benefit obligation ("PBO"), accumulated benefit obligation ("ABO") and fair value of the plan's assets [Abstract]
Projected benefit obligation	6,538,000	5,661,000
Accumulated benefit obligation	6,538,000	5,123,000
Fair value of plan assets	0	0
Summary of expected future benefit payments [Abstract]
2015	7,143,000
2016	0
2017	0
2018	0
2019	0
Years 2020 - 2024	$ 0