Benefit Plans - Assumptions Used to Determine Net Periodic (Benefit) Cost (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Astoria Bank | Pension Benefits
Assumptions used to determine net periodic cost
Discount Rate	4.09%	3.77%
Expected Return on Plan Assets	7.00%	8.00%
Astoria Bank | Astoria Excess and Supplemental Benefit Plans
Assumptions used to determine net periodic cost
Discount Rate	3.86%	3.60%
Astoria Bank | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate	3.67%	3.47%
Astoria Bank | Astoria Bank Retiree Health Care Plan
Assumptions used to determine net periodic cost
Discount Rate	4.25%	3.89%
Greater Directors’ Retirement Plan | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate	3.30%	3.12%
LIB Directors’ Retirement Plan | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate	0.95%	0.59%