Reconciliation of the Beginning and End of the Period Equity Accounts (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedules Of Reconciliation Of Beginning And End Of Period Equity Accounts [Line Items]
Balance at December 31, 2011			$ 697,890
Net income	74,113	17,281	147,427	44,478
Other comprehensive income	8,433	11,585	22,766	44,682
Dividends payable to noncontrolling shareholders			(3,495)
Acquisition of noncontrolling shareholders' interest			(71)
Stock compensation plans, including tax benefit of $1,764			10,810
Cash dividends-$.315 per share			(19,650)
Balance at September 30, 2012	877,601		877,601
Total Parent Stockholders' Equity
Schedules Of Reconciliation Of Beginning And End Of Period Equity Accounts [Line Items]
Balance at December 31, 2011			577,801
Net income			147,427
Other comprehensive income			21,205
Acquisition of noncontrolling shareholders' interest			(71)
Stock compensation plans, including tax benefit of $1,764			10,810
Cash dividends-$.315 per share			(19,650)
Balance at September 30, 2012	737,522		737,522
Noncontrolling Shareholders' Interests in Consolidated Subsidiaries
Schedules Of Reconciliation Of Beginning And End Of Period Equity Accounts [Line Items]
Balance at December 31, 2011			120,089
Net income			21,924
Other comprehensive income			1,561
Dividends payable to noncontrolling shareholders			(3,495)
Balance at September 30, 2012	$ 140,079		$ 140,079