Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 35,497	$ 41,976	$ 35,710	$ 31,555	$ 25,171	$ 29,471	$ 42,820	$ 37,110	$ 144,738	$ 134,572	$ 95,128
Denominator:
Basic weighted average shares outstanding	58,295,717	58,400,060	58,486,192	58,543,478	58,603,537	58,741,973	58,760,753	58,855,156	58,430,597	58,739,670	58,785,118
Effect of dilutive securities:
Diluted weighted average shares outstanding	58,512,733	58,604,603	58,687,540	58,829,177	58,936,795	59,084,117	59,051,413	59,199,622	58,657,749	59,067,302	59,150,920
Basic earnings per share	$ 0.61	$ 0.72	$ 0.61	$ 0.54	$ 0.43	$ 0.50	$ 0.73	$ 0.63	$ 2.48	$ 2.29	$ 1.62
Diluted earnings per share	$ 0.61	$ 0.72	$ 0.61	$ 0.54	$ 0.43	$ 0.50	$ 0.73	$ 0.63	$ 2.47	$ 2.28	$ 1.61
Stock appreciation rights [Member]
Effect of dilutive securities:
Dilutive securities									124,425	176,700	198,642
Restricted stock [Member]
Effect of dilutive securities:
Dilutive securities									102,727	150,932	167,160