Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of share-based compensation expense

Share-based compensation expense was as follows:

For the years ended December 31,	2017		2016		2015
Stock options, net of estimated forfeitures	$	50,753	$	27,543	$	23,120
Restricted stock awards	14,035		10,528		11,000
Total non-cash stock compensation	64,788		38,071		34,120
Deferred compensation arrangement	—		738		4,901
Total	$	64,788	$	38,809	$	39,021

Summary of stock options activity

The following tables summarize the stock option activity and the assumptions used to record the related share-based compensation expense for the years ended December 31, 2017, 2016 and 2015:

	2017						2016						2015
	Options		Weighted Average Exercise Price		Aggregate Intrinsic Value		Options		Weighted Average Exercise Price		Aggregate Intrinsic Value		Options		Weighted Average Exercise Price		Aggregate Intrinsic Value
Outstanding at January 1	10,928		$	21.81	$	4,350	11,427		$	26.12	$	20,339	10,919		$	25.84	$	48,851
Granted	4,283		$	19.01			303		$	23.29			1,447		$	26.72
Exercised	—		$	—	$	—	(245	)	$	19.57	$	899	(460	)	$	18.76	$	3,365
Forfeited or expired	(5,308	)	$	18.34			(557	)	$	23.78			(479	)	$	28.52
Outstanding at December 31	9,903		$	19.30	$	—	10,928		$	21.81	$	4,350	11,427		$	26.12	$	20,339
Exercisable at December 31	8,606		$	19.38	$	—	9,004		$	21.48	$	4,350	8,293		$	24.32	$	20,328
Vested and expected to vest	9,847		$	19.31	$	—	10,790		$	21.79	$	4,350	11,110		$	26.08	$	20,339

Summary of stock option plans, by exercise price range

	Options Outstanding		Options Exercisable		Assumption Range*
Exercise Prices	Number of Shares	Weighted Average Remaining Contractual Terms (Years)	Number of Shares	Weighted Average Remaining Contractual Terms (Years)	Risk-Free Interest Rate	Expected Terms in Years	Expected Volatility
Year Ended December 31, 2017
$14.58 - $19.56	6,500	4.58	5,549	4.22	0.33% - 3.31%	2.03 -10.00	32.18% - 69.74%
$21.00 - $21.28	693	2.18	347	0.66	0.43% - 3.60%	2.11 - 6.67	33.24% - 57.79%
$21.32 - $21.52	1,776	2.14	1,776	2.14	0.68% - 2.61%	3.38 - 6.55	38.16% - 69.74%
$21.68 - $22.32	221	1.94	221	1.94	0.57% - 3.03%	2.18 - 6.52	36.78% - 52.47%
$22.88 - $31.92	713	3.76	713	3.76	0.73% - 2.86%	4.00 - 6.52	39.03% - 53.80%
Year Ended December 31, 2016
$18.36 - $19.56	3,601	0.80	3,601	0.80	0.32% - 4.20%	1.90 - 6.95	26.85% - 52.47%
$20.16 - $21.28	353	1.66	353	1.66	0.42% - 3.60%	2.11 - 6.52	33.24% - 52.47%
$21.48 - $21.52	438	3.81	438	3.81	0.68% - 2.63%	3.38 - 6.58	38.16% - 52.47%
$21.68 - $22.32	320	3.10	320	3.10	0.57% - 3.03%	2.18 - 6.52	36.78% - 52.47%
$22.40 - $31.92	6,216	7.07	4,291	6.71	0.73% - 2.86%	4.00 - 7.12	39.03% - 58.84%
Year Ended December 31, 2015
$18.36 - $19.56	3,790	1.80	3,790	1.80	0.32% - 4.20%	1.90 - 6.95	26.85% - 52.47%
$20.16 - $21.28	353	2.70	353	2.70	0.42% - 3.60%	2.11 - 6.52	33.24% - 52.47%
$21.48 - $21.52	516	4.80	512	4.80	0.68% - 2.63%	3.38 - 6.58	38.16% - 52.47%
$21.68 - $22.32	344	4.10	344	4.10	0.57% - 3.03%	2.18 - 6.52	36.78% - 52.47%
$22.88 - $31.92	2,634	8.20	1,108	7.14	0.73% - 2.86%	4.00 - 6.52	39.03% - 58.84%
$34.52	3,788	7.80	2,184	7.80	1.76% - 2.07%	6.02 - 7.12	51.51% - 53.51%

* The expected dividend yield is zero for all options in all years.

Summary of non-vested restricted stock and restricted stock units activity

The following table summarizes the non-vested restricted stock and restricted stock units activity for the years ended December 31, 2017, 2016 and 2015:

	2017				2016				2015
	Shares		Weighted Average Grant Date Fair Value		Shares		Weighted Average Grant Date Fair Value		Shares		Weighted Average Grant Date Fair Value
Non-vested at January 1	1,038		$	25.97	865		$	29.6	694		$	32.48
Granted	1,337		$	16.65	655		$	23.27	449		$	26.28
Vested	(328	)	$	22.35	(386	)	$	29.36	(215	)	$	31.48
Forfeited	(397	)	$	23.33	(96	)	$	26.51	(63	)	$	31.08
Non-vested at December 31	1,650		$	19.74	1,038		$	25.97	865		$	29.6