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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings per common share:
Net earnings	$ 38,558	$ 29,683	$ 108,844	$ 86,560
Less: Net earnings allocated to restricted stock	96	107	298	325
Net earnings allocated to common shareholders	$ 38,462	$ 29,576	$ 108,546	$ 86,235
Weighted average shares outstanding	126,574	109,754	115,533	109,280
Basic earnings per common share	$ 0.30	$ 0.27	$ 0.94	$ 0.79
Diluted earnings per common share:
Net income allocated to common shareholders	$ 38,462	$ 29,576	$ 108,546	$ 86,235
Weighted average shares outstanding	126,574	109,754	115,533	109,280
Incremental shares from assumed exercise of outstanding options	363	365	397	392
Diluted weighted average shares outstanding	126,937	110,119	115,930	109,672
Diluted earnings per common share	$ 0.30	$ 0.27	$ 0.94	$ 0.79