Income Tax - Income Tax Expense Differs from Computed Income Tax at Statutory Rates (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Computed income tax at statutory rates	$ 43,753	$ 38,674	$ 23,477
Benefit of net tax-exempt interest income	(126)	(50)	(56)
Differences in tax rates due to multiple jurisdictions	1,058	(678)	2,353
Tax (benefit) expense due to a change in estimate	(84)	467	(334)
Effect of income subject to tax-exemption grant	(31,424)	(26,260)	(16,832)
Unrecognized tax (benefit) expense	(32)	443	(3,828)
Other	(170)	0	0
Income tax expense	$ 12,975	$ 12,596	$ 4,780