Fair Value Measurements Fair Value of Assets Measured on Recurring Basis Using Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 13,419	$ 16,134
Net unrealized gains included in other comprehensive income	505	1,635
Net unrealized gains (losses) included in other expense	(3,382)
Issuances	(75,074)
Settlements and derivative redesignation	76,747	(4,350)
Acquisitions	(59,947)
Ending Balance	(47,732)	13,419
The amount of total unrealized gains for the period included in other comprehensive income attributable to the change in accumulated other comprehensive losses relating to assets still held at the end of period	397	1,059
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	13,419	16,134
Net unrealized gains included in other comprehensive income	505	1,635
Net unrealized gains (losses) included in other expense	0
Issuances	0
Settlements and derivative redesignation	(2,250)	(4,350)
Acquisitions	0
Ending Balance	11,674	13,419
The amount of total unrealized gains for the period included in other comprehensive income attributable to the change in accumulated other comprehensive losses relating to assets still held at the end of period	397	1,059
Derivative
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	0
Net unrealized gains included in other comprehensive income	0	0
Net unrealized gains (losses) included in other expense	(3,382)
Issuances	(75,074)
Settlements and derivative redesignation	78,997	0
Acquisitions	0
Ending Balance	541	0
The amount of total unrealized gains for the period included in other comprehensive income attributable to the change in accumulated other comprehensive losses relating to assets still held at the end of period	0	0
Accrued Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisitions	(59,947)
Ending Balance	$ (59,947)