Stock-Based Compensation Plans (Narrative) (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended							9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Two Thousand And Seven Plan [Member]	May 31, 2011 Two Thousand And Seven Plan [Member]	May 31, 2009 Two Thousand And Seven Plan [Member]	Sep. 30, 2013 Two Thousand And Seven Plan [Member] Minimum [Member]	Sep. 30, 2013 Two Thousand And Seven Plan [Member] Maximum [Member]	Sep. 30, 2013 Nineteen Ninety Seven Plan [Member]	Sep. 30, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member] Minimum [Member]	Sep. 30, 2013 Restricted Stock [Member] Maximum [Member]	Sep. 30, 2013 Ltip Awards [Member]	Sep. 30, 2013 Ltip Awards [Member] Minimum [Member]	Sep. 30, 2013 Ltip Awards [Member] Maximum [Member]	Sep. 30, 2013 Performance Shares [Member]	Dec. 31, 2012 Performance Shares [Member]	Sep. 30, 2012 Performance Shares [Member]	Dec. 31, 2011 Performance Shares [Member]	Sep. 30, 2013 Performance Shares [Member] Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved for issuance					500,000
Shares additionally approved for issuance						2,860,000	325,000
Shares available for future grants					695,363
Award vesting period, maximum, years								3 years	5 years						1 year	5 years	3 years
Share based payment award options term					7 years					10 years							7 years
Percentage of performance based award payouts																		0.00%	200.00%
Allocated Share-based Compensation Expense	$ 2,000,000	$ 2,600,000	$ 6,500,000	$ 7,200,000
Weighted average grant date fair value per share of options granted	$ 17.49	$ 14.55
Aggregate intrinsic value of options exercised		$ 4,900,000	$ 777,000
Maximum number of performance-vested shares that could be issued											187,840	314,226	321,284	336,709						232,376	153,915	207,388	72,158	625,000