XML 67 R94.htm IDEA: XBRL DOCUMENT v2.4.0.6
Stock - Based Compensation - Performance based units earned under long-term incentive plan (Detail) (USD $)
12 Months Ended
Dec. 31, 2010
Dec. 31, 2012
Performance stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Nonvested at January 1, 2012   61,450
Restricted stock units,earned   307,813
Restricted stock units,vested (183,961) (154,129)
Accrued dividend equivalents   1,489
Nonvested at December 31, 2012   216,623
Weighted average grant date fair value, nonvested, beginning Balance   $ 18.60
Weighted average grant date fair value, earned   $ 15.63
Weighted average grant date fair value, vested   $ 16.84
Weighted average grant date fair value, accrued dividend equivalents   $ 17.74
Weighted average grant date fair value, nonvested, ending balance   $ 15.63