Employee Benefit Plans - Summary of Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Number of shares available for stock options (in shares)	83,201	105,100
Issuance of common stock (in shares)	23,163	18,314	25,024
Weighted Average Number of Shares Issued (Redeemed), Basic (in shares)	46,550
Forfeiture Of Shares Of Common Stock Shares (in shares)	1,264	1,042	1,142
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value	$ 41,510
Number of Shares
Options Outstanding Beginning Balance (in shares)	19,380	19,380	25,260
Granted (in shares)	0	0	0
Exercised (in shares)	0	0	(5,880)
Options Outstanding Ending Balance (in shares)	19,380	19,380	19,380	25,260
Weighted- Average Exercise Price
Options Outstanding Weighted Average Exercise Price Beginning Balance (in dollars per share)	$ 29.92	$ 29.92	$ 26.98
Options Outstanding Weighted Average Exercise Price Ending Balance (in dollars per share)	$ 29.92	$ 29.92	$ 29.92	$ 26.98
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term	3 years 11 days	4 years 11 days	5 years 11 days	4 years 8 months 19 days
Aggregate Intrinsic Value (In Thousands)
Aggregate Intrinsic Value	$ 580	$ 580	$ 580	$ 681