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Common Stock (Details) - USD ($) | 3 Months Ended | 54 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Mar. 31, 2016 | Dec. 31, 2015 | Oct. 28, 2015 | Oct. 23, 2014 | Dec. 05, 2013 | Sep. 26, 2011
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Common stock, outstanding | 60,681,075 |  | 60,681,075 | 61,067,868 |  |  |  |
Common stock, issued | 198,127 | 178,928 |  |  |  |  |  |
Stock repurchased (in US dollars) | $ 26,076,000 | $ 21,148,000 |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Number of shares repurchased |  |  | 10,500,000 |  |  |  |  |
Stock repurchased (in US dollars) | 6,000 | $ 5,000 | $ 421,900,000 |  |  |  |  |
Remaining authorized repurchase amount (in US dollars) | $ 228,100,000 |  | $ 228,100,000 |  |  |  |  |
Common Stock [Member] | RepurchaseProgramSep262011 |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Stock repurchase, authorized amount (in US dollars) |  |  |  |  |  |  |  | $ 100,000,000
Common Stock [Member] | RepurchaseProgramDec052013 |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Stock repurchase, authorized amount (in US dollars) |  |  |  |  |  |  | $ 100,000,000 |
Common Stock [Member] | RepurchaseProgramOct232014 |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Stock repurchase, authorized amount (in US dollars) |  |  |  |  |  | $ 250,000,000 |  |
Number of shares repurchased | 600,000 |  |  |  |  |  |  |
Stock repurchased (in US dollars) | $ 26,100,000 |  |  |  |  |  |  |
Common Stock [Member] | RepurchaseProgramOct282015 |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |
Stock repurchase, authorized amount (in US dollars) |  |  |  |  | $ 200,000,000.0 |  |  |

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