Stock Based Compensation - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Granted (in shares)	0	0	0	0
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, at December 31, 2015 (in shares)			1,210,141
Number of Options, Granted (in shares)			0
Number of Options, Exercised (in shares)			(386,739)
Number of Options, Forfeited (in shares)			0
Number of Options, Outstanding, at September 30, 2016 (in shares)	823,402		823,402		1,210,141
Number of Options, Vested and exercisable at September 30, 2016 (in shares)	823,402		823,402
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, at December 31, 2015 (in dollars per share)			$ 16.31
Weighted-Average Exercise Price, Granted (in dollars per share)			0.00
Weighted-Average Exercise Price, Exercised (in dollars per share)			16.10
Weighted-Average Exercise Price, Forfeited (in dollars per share)			0.00
Weighted-Average Exercise Price, Outstanding, at September 30, 2016 (in dollars per share)	$ 16.41		16.41		$ 16.31
Weighted Average Exercise Price, Vested and exercisable at September 30, 2016 (in dollars per share)	$ 16.41		$ 16.41
Aggregate Intrinsic Value, Outstanding	$ 27,530		$ 27,530		$ 34,638
Weighted-Average Remaining Contractual Life (in years)			3 years 18 days		3 years 6 months
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2016	$ 27,530		$ 27,530
Weighted-Average Remaining Contractual Life, Vested and exercisable at September 30, 2016 (in years)			3 years 18 days