Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Schedule Of Significant Accounting Policies [Line Items]
Minimum amount of non-accrual loans individually evaluated for impairment	$ 22,329	$ 21,085
Delinquent status classification term	90 days
Threshold of membership investment component, percentage	0.125%
Threshold of membership investment component	$ 1
Activity based investment component as a percentage of outstanding advances	4.50%
Goodwill	$ 38,411	$ 38,411
ESOP repayment period (years)	30 years
Effect of non-vested restricted stock and stock options outstanding	787,673	1,550,285	1,343,498
Minimum
Schedule Of Significant Accounting Policies [Line Items]
Minimum amount of non-accrual loans individually evaluated for impairment	$ 500
Accounting Standards Update 2018-02
Schedule Of Significant Accounting Policies [Line Items]
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	0
Accounting Standards Update 2018-02 | Retained Earnings
Schedule Of Significant Accounting Policies [Line Items]
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	$ 892	$ 892
ASU 2016-02 | Subsequent Event
Schedule Of Significant Accounting Policies [Line Items]
Right-of-use asset				$ 43,400
Operating lease liability				$ 47,200
Building
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of significant classes of assets (years)	40 years
Furniture And Equipment | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of significant classes of assets (years)	5 years
Furniture And Equipment | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of significant classes of assets (years)	7 years
Software
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of significant classes of assets (years)	3 years