Stock Compensation Plans and Other Employee Benefit Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Options Outstanding [Roll Forward]
Outstanding at beginning of the period (in shares)	1,698,912	1,551,734	1,618,426
Granted (in shares)	0	562,166	502,517
Options outstanding in acquired plans (in shares)			16,364
Exercised (in shares)	(593,459)	(313,900)	(273,411)
Forfeited or canceled (in shares)	(20,697)	(101,088)	(312,162)
Outstanding at end of the period (in shares)	1,084,756	1,698,912	1,551,734
Exercisable (in shares)	562,810	703,892	720,580
Vested or expected to vest (in shares)	1,065,809
Stock Options, Weighted Average Strike Price [Roll Forward]
Outstanding at beginning of the period (in dollars per share)	$ 41.50	$ 41.32	$ 43.00
Granted (in dollars per share)	0.00	41.04	44.36
Options outstanding in acquired plans (in dollars per share)			21.18
Exercised (in dollars per share)	40.57	37.71	42.82
Forfeited or canceled (in dollars per share)	42.83	48.00	52.53
Outstanding at end of the period (in dollars per share)	41.98	41.50	41.32
Exercisable (in dollars per share)	41.82	$ 39.62	$ 37.64
Vested or expected to vest (in dollars per share)	$ 41.97
Stock Options Additional Disclosures
Outstanding, Remaining Contractual Term	4 years	4 years 7 months 6 days	4 years 4 months 24 days
Outstanding, Intrinsic Value	$ 43,817	$ 52,790	$ 11,433
Exercisable, Remaining Contractual Term	3 years 4 months	3 years 4 months 24 days	3 years 1 month 6 days
Exercisable, Intrinsic Value	$ 22,820	$ 23,195	$ 8,045
Vested or expected to vest, Remaining Contractual Term	4 years
Vested or expected to vest, Intrinsic Value	$ 43,056