Capital Stock (Details)				3 Months Ended						9 Months Ended		12 Months Ended
	Oct. 26, 2017 $ / shares	Feb. 03, 2017 USD ($) $ / shares	Jan. 02, 2017 $ / shares	Sep. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Feb. 24, 2016 USD ($)	Dec. 31, 2015 shares	Oct. 13, 2014 USD ($)	Dec. 31, 2012 shares
Class of Stock [Line Items]
Preferred stock authorized (shares)				40,000,000						40,000,000		40,000,000
Preferred stock par value (usd per share) | $ / shares				$ 0.001						$ 0.001		$ 0.001
Treasury stock (shares)				14,102,185						14,102,185		14,102,453
Special dividends declared to shareholders and warrant holders, $5.77 per share | $				$ 21,834,000	$ 21,816,000	$ 21,742,000	$ 22,510,000	$ 22,959,000	$ 23,215,000	$ 65,392,000	$ 68,684,000
Number of shares called by each warrant (shares)				1						1
Regular Cash Dividend
Class of Stock [Line Items]
Dividends declared per common share (usd per share) | $ / shares				$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.75	$ 0.75
Regular Cash Dividend | Subsequent Event
Class of Stock [Line Items]
Dividends declared per common share (usd per share) | $ / shares	$ 0.25
Special Cash Dividend
Class of Stock [Line Items]
Dividends declared per common share (usd per share) | $ / shares			$ 5.77	0.00			$ 0.00			$ 5.77	$ 0.00
Warrant, Dividends, Per Share, Cash Paid | $ / shares		$ 5.77
Common stock dividends (usd per share) | $ / shares		$ 5.77
Special dividends declared to shareholders and warrant holders, $5.77 per share | $		$ 499,000,000								$ 499,107,000
Regular Cash Dividend Restriction
Class of Stock [Line Items]
Dividends declared per common share (usd per share) | $ / shares				$ 0.25
Warrant
Class of Stock [Line Items]
Warrants issued (shares)				36,582						36,582						16,789,972
Warrant, exercise price, per share (usd per share) | $ / shares				$ 0.001						$ 0.001
Class A Common Stock
Class of Stock [Line Items]
Common stock, authorized (shares)				1,000,000,000						1,000,000,000		1,000,000,000
Common stock, par value (usd per share) | $ / shares				$ 0.001						$ 0.001		$ 0.001
Common stock, conversion ratio										1
Number of warrants exercised (shares)				46,802			0			91,650	132,066
Number of shares received				46,802						91,650	132,066
Number of shares of common stock issued (shares)				101,402,202						101,402,202		100,416,516
Shares authorized (shares) | $													$ 400,000,000		$ 400,000,000
Treasury stock acquired (shares)												6,432,455
Common stock repurchases | $										$ 0		$ 232,000,000
Share price (usd per share) | $ / shares												$ 36.08
Remaining authorized repurchase amount | $				$ 168,000,000						$ 168,000,000
Treasury stock acquired life to date (shares)														7,670,216
Class B Common Stock
Class of Stock [Line Items]
Common stock, authorized (shares)				1,000,000,000						1,000,000,000		1,000,000,000
Common stock, par value (usd per share) | $ / shares				$ 0.001						$ 0.001		$ 0.001
Common stock, conversion ratio										1
Number of shares converted (shares)										0	0
Number of warrants exercised (shares)										0	0
Number of shares of common stock issued (shares)				5,605						5,605		5,605
Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized (shares)				40,000,000						40,000,000