Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Mandated fees under Affordable Care Act	$ 7,222	$ 5,642

Represents the amount of mandated fees under the Affordable Care Act.

No definition available.

Name:	usic_MandatedFeesUnderAffordableCareAct
Namespace Prefix:	usic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration