Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 17, 2015	Apr. 01, 2015	Apr. 01, 2013	Apr. 30, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Apr. 01, 2010
Stockholders Equity Note [Line Items]
Dividends declared per common share (in USD per share)	$ 0.45				$ 0.45	$ 0.45	$ 0.9	$ 0.9
Restricted Stock Units Dividends Paid							$ 3.4	$ 3.1
Cogent Partners, LP
Stockholders Equity Note [Line Items]
Number of shares issued during acquisition, shares		779,454
Conditional consideration, shares		334,048
Additional paid-in capital		$ 11.9
Common Stock
Stockholders Equity Note [Line Items]
Repurchased shares for award (shares)							312,748	351,662
Average repurchase price of shares for award (USD per share)							$ 34.55	$ 51.85
Contingent Convertible Preferred Stock | Caliburn Acquisition
Stockholders Equity Note [Line Items]
Conversion to common stock shares if revenue targets are achieved (shares)									1,099,877
Performance stock fair value at acquisition date		$ 14.4	$ 32.5
Contingent Convertible Preferred Stock | Tranche One - Performance Stock | Caliburn Acquisition
Stockholders Equity Note [Line Items]
Conversion of Stock (shares)			659,926	659,926
Contingent Convertible Preferred Stock | Tranche Two - Performance Stock | Caliburn Acquisition
Stockholders Equity Note [Line Items]
Conversion to common stock shares if revenue targets are achieved (shares)		439,951
Restricted Stock Units
Stockholders Equity Note [Line Items]
Restricted stock units vested and issued as common stock (shares)							762,568	892,038
Additional Paid-in Capital | Cogent Partners, LP
Stockholders Equity Note [Line Items]
Additional paid-in capital		$ 11.9