Equity Compensation Plans (Summary of Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares:
Outstanding at December 31, 2015 (in shares)	463,000
Granted (in shares)	56,580	91,900	131,800
Exercised (in shares)	(76,333)	(166,175)	(277,006)
Forfeited/Cancelled (in shares)	(17,000)
Outstanding at December 31, 2016 (in shares)	427,000	463,000
Options exercisable at December 31, 2016 (in shares)	240,000
Unvested at December 31, 2016 (in shares)	187,000
Weighted-Average Exercise Price:
Outstanding at December 31, 2015 (in dollars per share)	$ 20.15
Granted (in dollars per share)	52.22
Exercised (in dollars per share)	15.18
Forfeited/Cancelled (in dollars per share)	19.31
Outstanding at December 31, 2016 (in dollars per share)	25.32	$ 20.15
Weighted-Average Exercise Price, Options exercisable at December 31, 2016 (in dollars per share)	15.66
Weighted-Average Exercise Price, Unvested at December 31, 2016 (in dollars per share)	$ 37.74
Weighted- Average Remaining Contractual Term (years)
Outstanding at December 31, 2016	6 years 10 months 24 days
Options exercisable at December 31, 2016	5 years 6 months 6 days
Unvested at December 31, 2016	8 years 9 months 15 days
Aggregate Intrinsic Value
Outstanding at December 31, 2016	$ 15,694
Options exercisable at December 31, 2016	11,097
Unvested at December 31, 2016	$ 4,597