Earnings Per Share Reconciliation - Schedule of Earnings Per Common Share Reconciliation (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings per common share:
Net earnings	$ 29,683	$ 25,448	$ 86,560	$ 74,353
Less: Net earnings allocated to restricted stock	107	98	325	305
Net earnings allocated to common shareholders	$ 29,576	$ 25,350	$ 86,235	$ 74,048
Weighted average shares outstanding	109,754	108,984	109,280	107,144
Basic earnings per common share	$ 0.27	$ 0.23	$ 0.79	$ 0.69
Diluted earnings per common share:
Net income allocated to common shareholders	$ 29,576	$ 25,350	$ 86,235	$ 74,048
Weighted average shares outstanding	109,754	108,984	109,280	107,144
Incremental shares from assumed exercise of outstanding options	365	386	392	403
Diluted weighted average shares outstanding	110,119	109,370	109,672	107,547
Diluted earnings per common share	$ 0.27	$ 0.23	$ 0.79	$ 0.69