Benefit Plans - Incentive Savings Plan (Narrative) (Details) - USD ($)		12 Months Ended
	Jan. 01, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Maximum contribution of pre-tax base salary (as a percent)		30.00%
Maximum contribution of pre-tax base salary		$ 18,000
Matching contributions equal to each employee's contributions (as a percent)				50.00%
Contributions matched not in excess employee's compensation (as a percent)				6.00%
Maximum contribution of participating employee's compensation (as a percent)	4.50%			3.00%
Total matching contributions		$ 4,000,000	$ 3,900,000	$ 2,200,000
Vesting period for contributions made by Astoria Bank		1 year
Incentive Savings Plan, Amended 2014, Scenario 1
Defined Contribution Plan Disclosure [Line Items]
Matching contributions equal to each employee's contributions (as a percent)	100.00%
Contributions matched not in excess employee's compensation (as a percent)	3.00%
Incentive Savings Plan, Amended 2015, Scenario 2
Defined Contribution Plan Disclosure [Line Items]
Matching contributions equal to each employee's contributions (as a percent)	50.00%
Incentive Savings Plan, Amended 2015, Scenario 2 | Minimum
Defined Contribution Plan Disclosure [Line Items]
Contributions matched not in excess employee's compensation (as a percent)	3.00%
Incentive Savings Plan, Amended 2015, Scenario 2 | Maximum
Defined Contribution Plan Disclosure [Line Items]
Contributions matched not in excess employee's compensation (as a percent)	6.00%