Stockholders' Equity (Tables)
 9 Months Ended
Sep. 30, 2016
Stockholders' Equity Attributable to Parent [Abstract]  
Schedule of Dividends Declared [Table Text Block]
The following table presents cash dividends declared by the Company on its common stock during the three months ended September 30, 2016, and the four immediately preceding quarters:
Declaration Date
 
Record Date
 
Payment Date
 
Cash Dividend Per Share
September 15, 2016
 
September 30, 2016
 
October 20, 2016
 
$
0.23

June 16, 2016
 
June 30, 2016
 
July 20, 2016
 
$
0.23

March 15, 2016
 
March 31, 2016
 
April 21, 2016
 
$
0.23

December 16, 2015
 
December 30, 2015
 
January 20, 2016
 
$
0.26

September 16, 2015
 
September 30, 2015
 
October 22, 2015
 
$
0.26
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Accumulated other comprehensive income at September 30, 2016 and December 31, 2015 was as follows:
(in thousands)
September 30,
2016
 
December 31,
2015
Available-for-sale securities
 
 
 
Unrealized gains
$
551,343

 
$
405,177

Unrealized losses
(12,900
)
 
(46,116
)
Accumulated other comprehensive income
$
538,443

 
$
359,061
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]
The following table summarizes reclassifications out of accumulated other comprehensive income for the three and nine months ended September 30, 2016 and 2015:
 
 
Affected Line Item in the Condensed Consolidated Statements of Comprehensive Income (Loss)
 
Amount Reclassified out of Accumulated Other Comprehensive Income
(in thousands)
 
 
 
Three Months Ended
September 30,
 
Nine Months Ended
September 30,
 
 
 
 
2016
 
2015
 
2016
 
2015
Other-than-temporary impairments on AFS securities
 
Total other-than-temporary impairment losses
 
$
1,015

 
$
238

 
$
1,822

 
$
535

Realized gains on sales of certain AFS securities, net of tax
 
Gain on investment securities
 
(30,396
)
 
(53,447
)
 
(54,652
)
 
(228,518
)
Total
 
 
 
$
(29,381
)
 
$
(53,209
)
 
$
(52,830
)
 
$
(227,983
)