Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income available to common shareholders	$ 35,710	$ 31,555	$ 42,819	$ 37,110	$ 67,265	$ 79,930
Denominator:
Basic weighted average shares outstanding	58,486,192		58,760,753		58,514,676	58,807,694
Effect of dilutive securities:
Diluted weighted average shares outstanding	58,687,540		59,051,413		58,758,201	59,125,258
Basic earnings per share	$ 0.61		$ 0.73		$ 1.15	$ 1.36
Diluted earnings per share	$ 0.61		$ 0.73		$ 1.14	$ 1.35
Stock appreciation rights and options [Member]
Effect of dilutive securities:
Dilutive securities	129,839		173,571		141,958	183,814
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	71,509		117,089		101,567	133,750