Stockholders' Equity - Reconciliation of the Beginning and End of the Period Equity Accounts (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule Of Stockholders Equity [Line Items]
Beginning Balance			$ 908,416
Net income	35,486	51,746	91,566	73,314
Other comprehensive income	12,065	1,595	21,197	14,334
Dividends payable to noncontrolling shareholders			(9,790)
Stock compensation plans, including tax benefit of $145			4,464
Cash dividends - $.210 per share			(13,296)
Ending Balance	1,015,428		1,015,428
Total Parent Stockholders' Equity [Member]
Schedule Of Stockholders Equity [Line Items]
Beginning Balance			757,624
Net income			91,566
Other comprehensive income			19,446
Stock compensation plans, including tax benefit of $145			4,464
Cash dividends - $.210 per share			(13,296)
Ending Balance	859,804		859,804
Noncontrolling Shareholders' Interests in Consolidated Subsidiaries [Member]
Schedule Of Stockholders Equity [Line Items]
Beginning Balance			150,792
Net income			12,871
Other comprehensive income			1,751
Dividends payable to noncontrolling shareholders			(9,790)
Ending Balance	$ 155,624		$ 155,624