Common Stock - Additional Information (Detail) - USD ($)		1 Months Ended	2 Months Ended	6 Months Ended	10 Months Ended	12 Months Ended			29 Months Ended
	Feb. 13, 2015	Aug. 31, 2014	Feb. 19, 2016	Feb. 12, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Feb. 20, 2015	Aug. 06, 2014
Equity, Class of Treasury Stock [Line Items]
Amount paid to counter party under share repurchase program						$ 107,999,000	$ 108,821,000	$ 200,000,000
Common stock repurchased, shares						3,127,527			12,230,829
Share repurchase, weighted average price						$ 34.53			$ 34.08
Common shares reserved for compensation plans and contributions					8,466,764	8,466,764			8,466,764
Share Repurchase Program, August 6, 2014
Equity, Class of Treasury Stock [Line Items]
Amount paid to counter party under share repurchase program		$ 200,000,000
Percentage of common shares initially delivered under share repurchase program											80.00%
Share repurchase, weighted average price						$ 31.49
Share Repurchase Program, August 6, 2014 | JP Morgan Securities LLC
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized (up to)											$ 200,000,000
Amount paid to counter party under share repurchase program				$ 200,000,000
Common stock repurchased, shares	784,694	5,567,154		6,351,848
Share Repurchase Program, August 6, 2014 | Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized (up to)											$ 200,000,000
Share Repurchase Program, February 20, 2015
Equity, Class of Treasury Stock [Line Items]
Amount paid to counter party under share repurchase program			$ 17,622,000				$ 108,821,000
Common stock repurchased, shares			497,094				2,751,454
Share repurchase, weighted average price			$ 35.45				$ 39.55
Share repurchase, remaining amount authorized							$ 91,261,000
Share Repurchase Program, February 20, 2015 | Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized (up to)										$ 200,000,000
Share Repurchase Program, February 19, 2016
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized (up to)					$ 200,000,000	$ 200,000,000			$ 200,000,000
Amount paid to counter party under share repurchase program					$ 90,377,000
Common stock repurchased, shares					2,630,433
Share repurchase, weighted average price					$ 34.36
Share repurchase, remaining amount authorized					$ 109,702,000	$ 109,702,000			$ 109,702,000
Share Repurchase Program, February 19, 2016 | Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase, amount authorized (up to)			$ 200,000,000
Share repurchase, remaining amount authorized			$ 73,654,000