Fair Value - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jul. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Transfers between level 1 and level 2	$ 0	$ 0	$ 0	$ 0
Fair value measurements transfers into or out of Level 3			0	0	0	0
Investments, available-for-sale	132,762		132,762		139,046
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, available-for-sale	$ 0		$ 0	$ 0	$ 0	$ 0