Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 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)	185,798	136,413
Forfeited share equivalents (in shares)	(9,022)	(9,896)
Vested share equivalents (in shares)	(138,752)	(114,616)
Ending balance (in shares)	500,454	487,248
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	9,526	8,598
Forfeited share equivalents	463	624
Vested share equivalents	6,939	7,209
Ending balance	$ 25,658	$ 30,711
Market price of Company's stock (in usd per share)	$ 51.27	$ 63.03