Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Total Share Equivalents [Roll Forward]
Beginning balance (in shares)	462,430	475,347
Granted (in shares)	200,761	162,740
Forfeited share equivalents (in shares)	(27,267)	(28,728)
Vested share equivalents (in shares)	(158,491)	(138,678)
Ending balance (in shares)	477,433	470,681
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Value of Share Equivalents [Roll Forward]
Beginning balance	$ 25,466	$ 30,826
Granted	13,475	9,473
Forfeited share equivalents	1,830	1,672
Vested share equivalents	8,161	8,832
Ending balance	$ 32,045	$ 27,398
Market price of Company's stock (in usd per share)	$ 67.12	$ 58.21