Employee Share Plans - Stock Award Activity (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2017 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding Beginning balance, Number of Options | shares	4,376
Exercised, Number of Options | shares	(335)
Expired or canceled, Number of Options | shares	(3)
Outstanding Ending balance, Number of Options | shares	4,038
Exercisable Ending balance, Number of Options | shares	1,878
Outstanding Beginning balance, Weighted Average Exercise Price Per Share | $ / shares	$ 8.02
Exercised, Weighted Average Exercise Price Per Share | $ / shares	7.32
Expired or canceled, Weighted Average Exercise Price Per Share | $ / shares	6.52
Outstanding Ending balance, Weighted Average Exercise Price Per Share | $ / shares	8.08
Exercisable Ending balance, Weighted Average Exercise Price | $ / shares	$ 7.04
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding Beginning balance, Number of shares | shares	827
Granted, Number of shares | shares	70
Exercised, Number of shares | shares	(90)
Outstanding Ending balance, Number of shares | shares	807
Outstanding Beginning balance, Weighted Average Grant-Date Fair Value | $ / shares	$ 9.14
Granted, Weighted Average Grant-Date Fair Value | $ / shares	12.85
Exercised, Weighted Average Grant-Date Fair Value | $ / shares	9.40
Outstanding Ending balance, Weighted Average Grant-Date Fair Value | $ / shares	$ 9.43