Acquisition of Clifton Bancorp Inc. - Additional Information (Detail) - USD ($) $ in Thousands	Apr. 02, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017
Business Acquisition [Line Items]
Stockholders’ equity		$ 1,183,261	$ 1,236,081	$ 1,268,748	$ 989,273	$ 1,014,233	$ 1,057,181
Goodwill		$ 210,895		$ 210,895
Clifton Bancorp Inc. [Member]
Business Acquisition [Line Items]
Closing date	Apr. 02, 2018
Total assets	$ 1,610,000
Net loans receivable	1,120,000
Securities	326,900
Total liabilities	1,380,000
Deposits	949,800
Borrowings	414,100
Purchase price of acquisition	333,900
Stockholders’ equity	$ 330,700
Outstanding shares of Clifton common stock exchanged for shares of Company common stock	1.191
Issuance of shares of common stock to CSBK stockholders in conjunction with merger	25,400,000
Cash payment for consideration	$ 3,200
Goodwill recorded in merger	102,300
Goodwill	102,300
Core deposit intangible	$ 6,400