Summary of Restricted Stock Award Activity (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
		Apr. 30, 2015	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accumulated dividends paid upon vesting of restricted stock unit awards		$ 396
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period			375,585
Fair value of restricted shares that vested during the period			$ 12,742	$ 13,161
Income tax benefit recognized upon vesting of share based awards			4,748	3,311
Compensation expense recognized during the period			$ 2,901	$ 2,590
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period			143,872	123,769
Fair value of restricted shares that vested during the period			$ 4,747	$ 5,501
Accumulated dividends paid upon vesting of restricted stock unit awards	[1]		404	46
Income tax benefit recognized upon vesting of share based awards			1,993	2,303
Compensation expense recognized during the period			$ 2,217	$ 908

[1] Additional dividends of approximately $396 were paid during April 2015 related to the restricted stock unit awards that vested during the three months ended March 31, 2015.