Basis of Presentation and Significant Accounting Policies - Summary of Supplemental Cash Flow Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Supplemental Cash Flow Elements [Abstract]
Net cash paid for income taxes	$ 7,800	$ 1,695
Cash paid for interest expense	62	32
Acquisition-related activities:
Cash paid for acquisitions, excluding contingent consideration	4,596	47,520
Cash acquired in acquisitions, excluding restricted cash	(63)	(2,987)
Net cash paid for acquisitions	4,533	44,533
Non-cash investing and financing activities:
Non-cash acquisition of property under a build-to-suit lease	11,000
Property and equipment received and accrued in accounts payable	347	172
Total non-cash investing and financing activities	$ 11,347	$ 172