Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs) [Member]	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Shares
Outstanding, beginning balance (in shares) | shares	897,005
Granted (in shares) | shares	200,785
Vested and issued (in shares) | shares	(399,882)
Expired or forfeited (in shares) | shares	(53,116)
Outstanding, ending balance (in shares) | shares	644,792
Weighted-Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 46.82
Granted (in dollars per share) | $ / shares	68.69
Vested and issued (in dollars per share) | $ / shares	35.86
Expired or forfeited (in dollars per share) | $ / shares	55.04
Outstanding, ending balance (in dollars per share) | $ / shares	$ 59.77