Deposits (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Checking, non-interest bearing	$ 345,154	$ 321,858
Checking, interest bearing	599,668	565,399
Savings accounts	1,187,947	915,587
Certificates of deposit	389,610	364,971
Total deposits	$ 2,522,379	$ 2,167,815
Percentage Change, Checking, non-interest bearing	7.20%
Percentage Change, Checking, interest bearing	6.10%
Percentage Change, Savings accounts	29.70%
Percentage Change, Certificates of deposit	6.80%
Percentage change, Total	16.40%