Earnings Per Common Share ("EPS") - Schedule of Calculation of Numerator and Denominator in Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Distributed earnings allocated to common stockholders	$ 11,713	$ 8,497	$ 22,126	$ 16,606
Undistributed earnings allocated to common stockholders	33,063	17,989	62,544	35,156
Net income available to common stockholders	$ 44,776	$ 26,486	$ 84,670	$ 51,762
Denominator for basic EPS - weighted-average common shares	86,786	76,743	85,251	75,281
Effect of dilutive securities - stock options	729	723	750	700
Denominator for diluted EPS - weighted-average common shares and assumed conversions	87,515	77,466	86,001	75,981
Basic EPS	$ 0.52	$ 0.35	$ 0.99	$ 0.69
Diluted EPS	$ 0.51	$ 0.34	$ 0.98	$ 0.68