Employee Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Pension expense	$ 3.1	$ 2.4
Time-Based Restricted Shares | Long-term Incentive Plans
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation costs recognized in earnings	7.3	7.9
2006 Equity Incentive Plan
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation costs recognized in earnings	8.2	1.4
Enstar Group Limited Employee Share Purchase Plan
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation costs recognized in earnings	$ 0.1	$ 0.1