Income Taxes Income Taxes- Statutory Rate and Provisions for Income Taxes (Detail) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income taxes computed at federal statutory tax rate	$ 19,314	$ 12,723	$ 13,360
State income taxes, net of federal benefit	2,184	1,407	1,641
Nondeductible expenses	1,352	766	1,022
Other items	278	(99)	101
Income tax credit	(280)	(284)	(265)
Total Income Tax Expense (Benefit)	$ 22,848	$ 14,513	$ 15,859