Shareholders' Equity and Equity Compensation (Summary of Activity Under Stock Option Plans) (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Options Outstanding
Options outstanding at beginning of period (in shares)		393,347	893,139	1,765,947
Options exercised (in shares)		(178,759)	(476,793)	(847,340)
Options canceled (in shares)		(2,550)	(22,999)	(25,468)
Options outstanding at end of period (in shares)		212,038	393,347	893,139
Options exercisable at end of period (in shares)		204,394	364,770	721,645
Options vested at the end of the period (in shares)	[1]	211,809
Weighted- Average Exercise Price Per Share
Weighted Average Exercise Price Per Share, Outstanding at period start (in dollars per share)		$ 40.72	$ 43.23	$ 40.58
Weighted Average Exercise Price Per Share, Options exercised (in dollars per share)		40.90	44.6	37.82
Weighted Average Exercise Price Per Share, Options canceled (in dollars per share)		40.09	57.07	39.04
Weighted Average Exercise Price Per Share, Outstanding at period end (in dollars per share)		40.47	$ 40.72	$ 43.23
Weighted Average Exercise Price Per Share, Options exercisable at December 31, 2014		40.44
Weighted Average Exercise Price Per Share, Options vested at December 31, 2014 or expected to vest	[1]	$ 40.50
Weighted-Average Remaining Contractual Life in Years
Weighted-Average Remaining Contractual Life in Years, Options outstanding		3 years 2 months	3 years 9 months 24 days
Weighted-Average Remaining Contractual Life in Years, Options exercisable at December 31, 2014		3 years 1 month
Weighted-Average Remaining Contractual Life in Years, Options vested at December 31, 2014 or expected to vest	[1]	3 years 2 months
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Options outstanding		$ 2,557,193	$ 16,019,130
Aggregate Intrinsic Value, Options exercisable at December 31, 2014		2,478,456
Aggregate Intrinsic Value, Options vested at December 31, 2014 or expected to vest	[1]	$ 2,554,831

[1] In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.