Stock Incentive Plans - Summary of Restricted Stock Activity (Details) - Restricted Stock $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) grant $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Number of Restricted Stock
Outstanding as of beginning of period (in shares) | shares	1,708	1,293	982
Granted (in shares) | shares	427	1,048	556
Forfeited/Canceled (in shares) | shares	(206)	(353)	(59)
Vested (in shares) | shares	(574)	(280)	(186)
Outstanding as of end of period (in shares) | shares	1,355	1,708	1,293
Weighted Average Grant Date Fair Value
Outstanding as of beginning of period (in dollars per share) | $ / shares	$ 21.86	$ 20.89	$ 18.55
Granted (in dollars per share) | $ / shares	24.03	22.46	24.01
Forfeited/Canceled (in dollars per share) | $ / shares	21.70	21.04	19.37
Vested (in dollars per share) | $ / shares	21.60	20.67	18.28
Outstanding as of end of period (in dollars per share) | $ / shares	$ 22.67	$ 21.86	$ 20.89
Total Intrinsic Value of Restricted Stock Vested
Vested | $	$ 13,668	$ 6,434	$ 4,580
Number of annual grants | grant	2