Stock-based Compensation Expense - Fixed-Price Stock Options (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Shares
Outstanding Shares,Beginning Balance (in shares)	1,369,116
Granted (in shares)	222,939
Exercised (in shares)	(77,546)
Forfeited (in shares)	(26,133)
Expired (in shares)	(4,133)
Outstanding Shares, Ending Balance (in shares)	1,484,243	1,369,116
Exercisable, Ending Balance (in shares)	958,599
Weighted-Average Exercise Price
Outstanding Weighted-Average Exercise Price, Beginning Balance (in dollars per share)	$ 47.55
Granted (in dollars per share)	$ 63.84
Exercised (in dollars per share)	$ 34.99
Forfeited (in dollars per share)	$ 64.93
Expired (in dollars per share)	$ 62.60
Outstanding Weighted-Average Exercise (in dollars per share)Price, Ending Balance	$ 50.30	$ 47.55
Exercisable Weighted-Average Exercise Price, Ending Balance (in dollars per share)	$ 42.33
Weighted-Average Remaining Contractual Term (Years)
Weighted-Averaged Remaining Contractual Term, Beginning Balance	6 years 6 months	7 years
Weighted-Averaged Remaining Contractual Term, Ending Balance	6 years 6 months	7 years
Exercisable Weighted-Average Remaining Contractual Term, Ending Balance	5 years 4 months 24 days
Aggregate Intrinsic Value
Outstanding Aggregate Intrinsic Value, Beginning Balance	$ 22,795
Outstanding Aggregate Intrinsic Value, Ending Balance	17,887	22,795
Exercisable Aggregate Intrinsic Value, Ending Balance	$ 17,887