XML 203 R190.htm IDEA: XBRL DOCUMENT v3.8.0.1
Note Stock-based compensation (Summary of restricted stock activity under the incentive plan for members of management) (Detail) - Restricted Stock Units (RSUs) - Executive Officers - $ / shares
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward          
Granted 0 0 138,516 279,890  
Performance Based Shares          
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward          
Beginning Balance     383,982 495,731 495,731
Granted     212,200   344,488
Quantity adjusted by TSR factor     (39,414)   39,566
Vested     (188,399)   (487,784)
Forfeited         (8,019)
Ending Balance 368,369   368,369   383,982
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Additional Disclosures Abstract          
Non-vested at beginning of period     $ 26.35 $ 28.25 $ 28.25
Granted     42.57   25.86
Quantity adjusted by TSR factor     33.77   24.37
Vested     35.47   27.72
Forfeited         29.13
Non-vested at end of period $ 30.24   $ 30.24   $ 26.35