Reconciliation of Net Income and Shares Amounts in Computation of Basic and Diluted Net Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 20,594	$ 17,407	$ 39,306	$ 30,762
Earnings per share:
Basic	$ 0.27	$ 0.23	$ 0.52	$ 0.40
Effect of CESs		$ (0.01)	$ (0.01)	$ (0.01)
Diluted	$ 0.27	$ 0.22	$ 0.51	$ 0.39
Weighted average number of shares:
Basic	75,274	76,888	75,544	77,096
Effect of CESs	763	1,148	871	1,292
Diluted	76,037	78,036	76,415	78,388