Fair Value Measurements - OREO (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Sep. 13, 2013
Fair Value
Non-covered impaired loans	$ 5,317,615		$ 5,174,625
Covered impaired loans	346,169		378,762
Covered other real estate owned	78,890	$ 137,703	99,090	$ 136,945
Total Gains (Losses) of impaired loans	(3,407)	(2,687)
Covered
Fair Value
Covered impaired loans	346,169		378,762
Total Gains (Losses) of impaired loans	278	107
Noncovered
Fair Value
Non-covered impaired loans	5,317,615		5,174,625
Total Gains (Losses) of impaired loans	(3,685)	(2,794)
Estimate of Fair Value Measurement
Fair Value
Non-covered impaired loans	5,355,827		5,203,374
Covered impaired loans	484,424		527,201
Level 2 | Estimate of Fair Value Measurement
Fair Value
Non-covered impaired loans	463,987		602,968
Level 3 | Estimate of Fair Value Measurement
Fair Value
Non-covered impaired loans	4,891,840		4,600,406
Covered impaired loans	484,424		527,201
Non-recurring | Covered
Fair Value
Covered impaired loans	45,025
Covered other real estate owned	11,322
Total Gains (Losses) of impaired loans	332	3,218
Total Gains (Losses) of other real estate owned	(9,765)	(950)
Non-recurring | Noncovered
Fair Value
Non-covered impaired loans	39,722
Total Gains (Losses) of impaired loans	(33)	349
Total Gains (Losses) of other real estate owned		$ (28)
Non-recurring | Level 2 | Covered
Fair Value
Covered other real estate owned	11,322
Non-recurring | Level 2 | Estimate of Fair Value Measurement | Noncovered
Fair Value
Non-covered other real estate owned	500		400
Non-recurring | Level 3 | Covered
Fair Value
Covered impaired loans	45,025
Non-recurring | Level 3 | Noncovered
Fair Value
Non-covered impaired loans	39,722
Non-recurring | Level 3 | FNB | Covered | Bank
Fair value measurements
Acquired OREO					$ 135,200
Non-recurring | Level 3 | Estimate of Fair Value Measurement | Covered
Fair Value
Covered other real estate owned	$ 78,900		$ 99,100