Shareholders' Equity (Narrative) (Details)			1 Months Ended	3 Months Ended		12 Months Ended
	Oct. 01, 2016 USD ($) shares	Apr. 24, 2014	Jan. 31, 2015 shares	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Oct. 31, 2014 USD ($)
Class of Stock [Line Items]
Common stock, shares issued (in shares) | shares				140,592,409		142,025,720	140,592,409
Fair value of common stock issued				$ 140,592,000		$ 142,026,000	$ 140,592,000
Stock Repurchased During Period, Value						$ 263,084,000	$ 199,221,000		$ 88,113,000
Stock split, conversion ratio		0.1429
Common stock, shares authorized | shares				342,857,143		342,857,143	342,857,143
Repurchase of Common Stock 300 Million [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 300,000,000			$ 300,000,000
Stock repurchase program, period in force					15 months
Repurchase of Common Stock 300 Million [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock Repurchased During Period, Value						$ 262,900,000
Repurchase of common stock | shares						8,700,000
Stock repurchase program, repurchased amount				$ 37,100,000
Stock repurchase program, shares repurchased | shares				1,200,000
Open Market Transactions [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, repurchased amount						$ 212,900,000	$ 161,900,000	$ 175,000,000
Stock repurchase program, shares repurchased | shares						7,300,000	5,700,000	6,200,000
Accelerated Share Repurchase Program [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount										$ 75,000,000.0
Stock repurchase program, repurchased amount						$ 50,000,000
Stock repurchase program, shares repurchased | shares			392,000			1,400,000			2,500,000.0
Repurchase of Common Stock 250 Million [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, repurchased amount					$ 250,000,000.0
Stock repurchase program, shares repurchased | shares						9,100,000.0
Global One [Member]
Class of Stock [Line Items]
Consideration transferred	$ 30,000,000
Common stock, shares issued (in shares) | shares	821,000
Fair value of common stock issued	$ 26,592,000
Cash paid	$ 3,408,000