Capital Stock and Equity Awards - Summary of RSU Activity (Details) - RSUs - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Shares
Unvested, beginning of period (in shares)	178,882	196,800
Granted (in shares)	214,907	117,879
Vested (in shares)	(62,714)	(37,485)
Forfeited (in shares)	0	(19,743)
Unvested, end of period (in shares)	331,075	257,451
Shares
Unvested, beginning of period (in dollars per share)	$ 37.93	$ 24.38
Granted (in dollars per share)	39.81	42.17
Vested (in dollars per share)	40.90	32.07
Forfeited (in dollars per share)	0.00	24.06
Unvested, end of period (in dollars per share)	$ 38.59	$ 31.43
Vesting period (in years)	3 years
Non-employee directors
Shares
Vesting period (in years)	1 year
Minimum
Shares
Vesting period (in years)	1 year
Maximum
Shares
Vesting period (in years)	5 years