Retirement Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Matching Obligations in Connection with Plans Which are Funded in Cash and Typically Contributed to Plans [Abstract]
Defined contribution plan, recognized	$ 8,445	$ 8,267	$ 8,115
Employer contributions during the period	300	500	400
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Provision for expense in connection with ESOP	$ 2,200	1,800	4,400
Employee Stock Ownership Plan and Trust (ESOP) [Member]
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Additional shares contributed to ESOP (in shares)	58,000
Shares released from trust (in shares)	58,200
Total remaining balance of shares in the ESOP (in shares)	200
SERP Defined Benefit Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	$ 6,538	5,661
Service cost	0	164	180
Interest cost	218	277	235
Actuarial loss	854	436
Benefits paid	(7,610)	0
Benefit obligation at end of year	0	6,538	5,661
Unfunded status of the plan	0	(6,538)
Amounts recognized in the balance sheet [Abstract]
Accrued postretirement benefit liabilities	0	6,538
Accumulated other comprehensive loss (pre-tax) related to [Abstract]
Unrecognized net actuarial losses	0	1,389
Unrecognized prior service cost	0	0
Defined benefit retirement plan [Abstract]
Service cost	0	164	180
Interest cost	218	277	235
Amortization of prior service cost	0	0	28
Amortization of unrecognized loss	735	388	690
Settlement loss	1,509	0	0
Net periodic benefit cost	$ 2,462	$ 829	$ 1,133
Actuarial Assumptions used to Determine Costs and Benefit Obligations [Abstract]
Discount rates	2.88%	4.00%	4.90%
Salary increase			4.00%
Summary of Defined Benefit Pension Plan, Projected Benefit Obligation ("PBO"), Accumulated Benefit Obligation ("ABO") and Fair Value of the Plan's Assets [Abstract]
Projected benefit obligation	$ 0	$ 6,538
Accumulated benefit obligation	0	6,538
Fair value of plan assets	$ 0	$ 0