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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income available to common shareholders	$ 20,098	$ 7,787	$ 76,829	$ 55,217
Denominator:
Basic weighted average shares outstanding	29,404,049	29,295,284	29,385,722	29,419,958
Effect of dilutive securities:
Diluted weighted average shares outstanding	29,578,216	29,516,718	29,563,497	29,635,796
Basic earnings per share	$ 0.68	$ 0.27	$ 2.61	$ 1.88
Diluted earnings per share	$ 0.68	$ 0.26	$ 2.60	$ 1.86
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities	97,315	116,803	98,905	133,907
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	76,852	104,631	78,870	81,931