Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income available to common shareholders	$ 42,710	$ 47,218	$ 42,402	$ 41,976	$ 35,710	$ 31,555	$ 132,331	$ 109,241
Denominator:
Basic weighted average shares outstanding	115,773,030			116,802,366			115,921,463	116,952,860
Effect of dilutive securities:
Diluted weighted average shares outstanding	116,134,623			117,211,452			116,280,807	117,413,920
Basic earnings per share	$ 0.37			$ 0.36			$ 1.14	$ 0.94
Diluted earnings per share	$ 0.37			$ 0.36			$ 1.14	$ 0.93
Stock appreciation rights and options [Member]
Effect of dilutive securities:
Dilutive securities	202,113			230,350			187,767	266,060
Restricted stock [Member]
Effect of dilutive securities:
Dilutive securities	159,480			178,736			171,577	195,000