Other Assets - Summary of Other Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Benefits receivable related to retrospective reinsurance contracts	$ 21,734	$ 8,815
Deferred costs related to retrospective reinsurance contracts	413	194
Deferred offering costs on senior notes issued in 2013	3,819	4,305
Prepaid expenses	1,722	771
Other	4,857	1,729
Total other assets	$ 32,545	$ 15,814