Goodwill and Other Intangible Assets, Net - Amortization Expense Related to Client Lists and Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 14,478us-gaap_AmortizationOfIntangibleAssets	$ 13,535us-gaap_AmortizationOfIntangibleAssets	$ 11,459us-gaap_AmortizationOfIntangibleAssets
Operating Expenses [Member]
Finite-Lived Intangible Assets [Line Items]
Total amortization expense	14,462	13,520	11,443
Corporate General and Administrative Expenses [Member]
Finite-Lived Intangible Assets [Line Items]
Total amortization expense	$ 16	$ 15	$ 16