Income Taxes - Provision for Federal and State Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal									$ 15,043	$ 9,770	$ 9,273
State									1,098	972	961
Deferred:
Federal									(1,068)	(862)	7,350
State									(739)	263	133
Provision for federal and state income taxes, total	$ 3,384	$ 3,782	$ 3,669	$ 3,499	$ 3,922	$ 3,204	$ 191	$ 2,826	$ 14,334	$ 10,143	$ 17,717