Employee Benefits and Share-Based Compensation - Restricted Stock Activity (Details) - 2009 Plan - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Restricted Stock Units (RSUs)
Number of Shares
Outstanding at beginning of period (in shares)	505
Granted (in shares)	86
Vested (in shares)	(96)
Forfeited (in shares)	(11)
Outstanding and unvested at end of period (in shares)	484		505
Weighted-Average Grant Date Fair Value
Outstanding and unvested (in dollars per share)	$ 31.42
Granted (in dollars per share)	37.21	$ 28.09
Vested (in dollars per share)	28.88
Forfeited (in dollars per share)	32.17
Outstanding and unvested (in dollars per share)	$ 32.93		$ 31.42
Weighted-average remaining years, outstanding and unvested	1 year 4 months 24 days		1 year 7 months
Aggregate Intrinsic Value
Outstanding and unvested at end of period	$ 20,901		$ 17,135
Unrecognized compensation cost	$ 12,800
Weighted average period of compensation cost not yet recognized (in years)	2 years 6 months 29 days
Restricted Stock Awards
Number of Shares
Outstanding at beginning of period (in shares)	30
Granted (in shares)	24
Vested (in shares)	(30)
Forfeited (in shares)	0
Outstanding and unvested at end of period (in shares)	24		30
Weighted-Average Grant Date Fair Value
Outstanding and unvested (in dollars per share)	$ 31.57
Granted (in dollars per share)	41.10
Vested (in dollars per share)	31.58
Forfeited (in dollars per share)	0.00
Outstanding and unvested (in dollars per share)	$ 41.03		$ 31.57
Aggregate Intrinsic Value
Unrecognized compensation cost	$ 800
Weighted average period of compensation cost not yet recognized (in years)	10 months 21 days