Share-Based Payment Arrangements (Detail) - Stock Options Outstanding And Exercisable (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Options Outstanding [Member] | Range $8.90 to $13.63 [Member]
Number of Option Shares Outstanding	35,021
Weighted-Average Remaining Contractual Life (in yrs)	1 year 292 days
Weighted-Average Exercise Price (in Dollars per share)	$ 11.98
Options Outstanding [Member] | Range $14.00 to $16.88 [Member]
Number of Option Shares Outstanding	40,879
Weighted-Average Remaining Contractual Life (in yrs)	2 years 146 days
Weighted-Average Exercise Price (in Dollars per share)	$ 14.15
Options Outstanding [Member] | Range $17.00 to $19.54 [Member]
Number of Option Shares Outstanding	56,354
Weighted-Average Remaining Contractual Life (in yrs)	350 days
Weighted-Average Exercise Price (in Dollars per share)	$ 19.54
Options Outstanding [Member] | Range $20.77 to $23.90 [Member]
Number of Option Shares Outstanding	28,942
Weighted-Average Remaining Contractual Life (in yrs)	1 year 146 days
Weighted-Average Exercise Price (in Dollars per share)	$ 23.66
Options Outstanding [Member] | Range $24.26 to $28.50 [Member]
Number of Option Shares Outstanding	23,650
Weighted-Average Remaining Contractual Life (in yrs)	160 days
Weighted-Average Exercise Price (in Dollars per share)	$ 25.26
Options Outstanding [Member] | Range $29.35 to $31.90 [Member]
Number of Option Shares Outstanding	4,000
Weighted-Average Remaining Contractual Life (in yrs)	1 year 146 days
Weighted-Average Exercise Price (in Dollars per share)	$ 29.92
Options Outstanding [Member] | Range $32.28 to $38.71 [Member]
Number of Option Shares Outstanding	70,343
Weighted-Average Remaining Contractual Life (in yrs)	1 year 167 days
Weighted-Average Exercise Price (in Dollars per share)	$ 32.38
Options Outstanding [Member]
Number of Option Shares Outstanding	259,189
Weighted-Average Remaining Contractual Life (in yrs)	1 year 164 days
Weighted-Average Exercise Price (in Dollars per share)	$ 22.30
Options Exercisable [Member] | Range $8.90 to $13.63 [Member]
Number of Option Shares Outstanding	35,021
Weighted-Average Exercise Price (in Dollars per share)	$ 11.98
Options Exercisable [Member] | Range $14.00 to $16.88 [Member]
Number of Option Shares Outstanding	23,586
Weighted-Average Exercise Price (in Dollars per share)	$ 14.15
Options Exercisable [Member] | Range $17.00 to $19.54 [Member]
Number of Option Shares Outstanding	56,354
Weighted-Average Exercise Price (in Dollars per share)	$ 19.54
Options Exercisable [Member] | Range $20.77 to $23.90 [Member]
Number of Option Shares Outstanding	28,942
Weighted-Average Exercise Price (in Dollars per share)	$ 23.66
Options Exercisable [Member] | Range $24.26 to $28.50 [Member]
Number of Option Shares Outstanding	23,650
Weighted-Average Exercise Price (in Dollars per share)	$ 25.26
Options Exercisable [Member] | Range $29.35 to $31.90 [Member]
Number of Option Shares Outstanding	4,000
Weighted-Average Exercise Price (in Dollars per share)	$ 29.92
Options Exercisable [Member] | Range $32.28 to $38.71 [Member]
Number of Option Shares Outstanding	70,343
Weighted-Average Exercise Price (in Dollars per share)	$ 32.38
Options Exercisable [Member]
Number of Option Shares Outstanding	241,896
Weighted-Average Exercise Price (in Dollars per share)	$ 22.88