Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended			9 Months Ended					1 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Apr. 30, 2010	Sep. 30, 2013 Common Stock	Sep. 30, 2012 Common Stock	Sep. 30, 2013 Restricted Stock Units	Sep. 30, 2012 Restricted Stock Units	Apr. 30, 2010 Caliburn Acquisition [Member] Contingent Convertible Preferred Stock	Apr. 30, 2013 Tranche One - Performance Stock [Member] Caliburn Acquisition [Member]	Apr. 30, 2010 Tranche One - Performance Stock [Member] Caliburn Acquisition [Member] Contingent Convertible Preferred Stock	Apr. 30, 2010 Tranche Two - Performance Stock [Member] Caliburn Acquisition [Member] Contingent Convertible Preferred Stock
Stockholders Equity Note [Line Items]
Dividends declared per common share (in USD per share)	$ 0.45
Dividend equivalents paid on outstanding restricted stock units		$ 4.7	$ 4.2
Restricted stock units vested and issued as common stock (shares)							662,569	632,794
Repurchased shares for award (shares)					214,303	176,781
Average repurchase price of shares for award (USD per share)					$ 57.22	$ 45.21
Repurchased common stock (shares)					853,870	859,006
Average repurchase price of common stock (in USD per share)					$ 49.81	$ 37.84
Conversion to common stock shares if revenue targets are achieved (shares)									1,099,877			439,951
Conversion of Stock, Shares Converted										659,926
Revenue Target Period											3 years	5 years
Performance stock fair value at acquisition date				$ 32.5