Income Taxes (Components of income tax expense (benefit)) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current income taxes:
Federal									$ 17,890	$ 13,671	$ 15,391
State									4,140	3,103	3,824
Total current									22,030	16,774	19,215
Deferred income taxes:
Federal									10	554	2,743
State									(13)	254	605
Total deferred									(3)	808	3,348
Total income tax expense (benefit)	$ 6,372	$ 5,175	$ 5,014	$ 5,466	$ 4,086	$ 5,428	$ 2,722	$ 5,346	$ 22,027	$ 17,582	$ 22,563